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Discussion Starter #1
Please help me diagnose and correct this alternator whine. I am somewhat of a noob, so please be gentle.......

Car: 2001 BMW M5, battery is in the trunk
Setup: Kenwood DNX9980HD (double din GPS, top of the line a year or so ago, recently bought used for a reputable person), JL HD900/5, Knuconceptz "Krystal RCA Kables," 2 JL10W3 subs, all other speakers are stock for now, all speaker wire is stock EXCEPT speaker wires to the subs and speaker wires to focal crossovers which then tap into the stock speaker wire.

My car has OEM power cables running down the right side of my car. I stayed away from them and ran my RCAs down the left side of the car, in the floor, directly alongside the stock wiring which consists of speaker wires, digital signal wires, and only the German car Gods know what else. None of the OEM wiring was removed, just unplugged at the units and tapped into as required. The OEM setup has a dummy screen up front with the stereo head unit, amp, nav unit, and 6 disc changer in the trunk.

I tested all grounds and they are now showing 0 volts. The head unit is using the stock ground wire, not sure if this is a problem, but it read 0 volts. When I unplug the RCAs from the Kenwood head unit, the alternator whine is still present when I rev my engine. When I unplug the RCAs at the amp side, the whine goes away. I'm thinking maybe the RCAs are acting like an antenna since the whine is still there when unplugged from the head unit but still plugged into the amp??

What should I do? I've heard about RF filters, but heard they are not the best solution. Should I buy some cheap RCAs to run outside my car and see if that solves the problem to diagnose? If so, what solutions do I have? Try re-running the RCAs through the top of the car? I would really rather not remove stock wiring. My intentions were to be able to go back to stock if I ever sold the car or reasons I can't think of now, but would have the option. Thanks for the help!
 

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BMw's are notorious for being noisey.
Did u clean off the chassis ground? Where is your negative grounded ? The battery or the chassis bolt? (See first question.
Do you have a computer chip?
The last e90 I did had been chipped and it was a crappy ground on the chip that caused the noise.
 

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I would try another set of rca's not run in the car. But if it's radiated noise, it's a big pain in the ass to stop.
You may have to bandaid it with a ground loop isolator (PAC sni 1)
They are cheap and can help trouble shoot.
 

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Discussion Starter #4
The car is tuned, but not a different "chip," only the software is changed and I relocated the air temperature intake gauge.

From the amp, I had a short ground going to the chassis. It read 0 volts, but as an experiment, I got a 6 ft. Ground wire and grounded where my battery bolts to the chassis. It reads 0v, but did not eliminate the noise.

For the PAC SNI 1, is that just for trouble shooting, or the possible solution? My understanding is RF filters filter part of ALL signals, and reduce the signal that I WANT going to my amp. I'm not looking to win any competitions, but I do want good, clean, powerful sound.
 

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Honestly they don't the filters don't do that badly on signal. They have even been hidden in competition cars before.
did u try to ground at the battery?
I would try that.
Did ur piggy back have to be grounded?
The e90 had a juice box on it that did.
 

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yeah my BMW was a PITA when it came to noise. Assuming all wiring is done correctly and you still have whine. In my case only two things fixed it...symibilink cables to zapco ref amps. AND a MSD noise capacitor right after the alternator. Noise Capacitor, 26 Kufd - 8830

power in and out of one terminal, and ground to the chassis off the other terminal. This is the only other thing that fixed the alternator whine.
 

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I tried a lot of different things on my E46
1. Firstly I earthed the head unit at the same point as my amp(noise improved)
2. Moved the RCAs as they were running near fuel pump (didn't make much difference)
3. Ran constant live to the head unit direct from battery ( really improved things)
I still have a very small whine but when I get the time going to try a cap at the alternator

Forgot to mention I also had a problem once when I mounted my amp on a metal bracket so mounted it on Mdf and mounted this to the bracket...
 

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Discussion Starter #10
Thanks all, I will try these things. To answer some questions, my amp and battery ground are currently tied into the same point on the chassis, which is the original battery ground location. My amp is screwed into a piece of plywood, which is bolted to the OEM metal amp bracket.

How close would the cap have to be to my alternator? I'm not sure how easy/difficult it would be to mount right at the alternator. Guess I have some homework to do.
 

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The main power cables in the e39 are run down the left side back to the battery, then from the battery back up the right side to power the fuse panel. Though I don't think that's the source of your problem. Others on here have given very good suggestions that I may end ip using when I get my system going. I don't have to deal with BMW mechanical bits though.
 

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I've got a bimmer also and my build starts as soon as the weather warms up.

From reading a lot I've seen many owners run the RCAs down the MIDDLE of the car as an alternative to the left side which cuts down the noise. Don't know if that's an option for you as the console, and seats may need to be removed to run it under the carpet.

When I do my install I'm running them down the middle to avoid issues.
 

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Discussion Starter #14
Does your car have a jump start point under the bonnet ?
A lot of people mount a cap close to this..
Ah, excellent point, yes it does. Would I need to install the cap in a specific configuration, as in "upstream" or "downstream" of any of my cars components, i.e. alternator or whatever?
 

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Discussion Starter #15
The main power cables in the e39 are run down the left side back to the battery, then from the battery back up the right side to power the fuse panel. Though I don't think that's the source of your problem. Others on here have given very good suggestions that I may end ip using when I get my system going. I don't have to deal with BMW mechanical bits though.
Is it possible the M5 is an exception to this? I see some large red power wires with a hub (distribution block?) on the right side of my trunk and those wires run up the right side of my car. I don't see any large power cables on the left (U.S. driver's side).
 

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Discussion Starter #16
I've got a bimmer also and my build starts as soon as the weather warms up.

From reading a lot I've seen many owners run the RCAs down the MIDDLE of the car as an alternative to the left side which cuts down the noise. Don't know if that's an option for you as the console, and seats may need to be removed to run it under the carpet.

When I do my install I'm running them down the middle to avoid issues.
Running down the middle is a possibility if I can determine the problem, but it will be a pain to reroute my wires. Are RCAs the ONLY wires I would need to reroute? I have a power signal wire, bass booster, and antenna extender all running together with the stock wiring.

Wait, does a power signal wire have enough power to cause interference?? It reads around 0.2-0.3v.
 

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The cap should go on the output post of your alternator (try a 4700uF polarized cap) with the - side attached to chassis ground (the case of the alternator is as good a point for this as any). I'd do that first. Then, if that doesn't get rid of it, try the ground loop isolator. The PAC SNI1 is a good one. Expect to pay 20 bucks for one. You want one that has transformers inside, not just caps.

FWIW, ground loop isolators aren't a band-aid. Isolating single ended outputs and inputs using transformers is as valid as any other solution--except a completely different signal configuration where audio negative isn't chassis ground (like symbilink or the configuration the OEM's use, which is simply balanced outputs and floating differential inputs).
 

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The wires turn 90* in the rear footwell and run up the right side in the trunk, but it starts at the driver side footwell/firewall. As far as I know, all e39s are wired this way even the touring.

Center console or above the headliner are the only ways to run wires that will completely avoid any large power wires. But I doubt EMI is playing any significant roll in your issue.
 

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Running down the middle is a possibility if I can determine the problem, but it will be a pain to reroute my wires. Are RCAs the ONLY wires I would need to reroute? I have a power signal wire, bass booster, and antenna extender all running together with the stock wiring.

Wait, does a power signal wire have enough power to cause interference?? It reads around 0.2-0.3v.
I talked to an installer and he explained it like this:

RCAs are low voltage signals THUS they need to be a little more shielded and are susceptable to interference. Speaker wires and the like are high voltage and are less susceptable to interference.

Don't quote me exact, it mentioned something along those lines so according to what he told me, it's just the RCA's you'd have to reroute.
 

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Ah, excellent point, yes it does. Would I need to install the cap in a specific configuration, as in "upstream" or "downstream" of any of my cars components, i.e. alternator or whatever?
This jump start point will have a cable bolted to it direct from the battery
Disconnect the battery
Remove alt cable from jump start point
Connect this cable to pos on cap along with a very short run of 4guage with a ring terminal at each end and connect other end to jump start point
Run another short length of 4guage terminated with ring terminals from the caps neg connection to chassis close by making sure its to clean bare metal
Job done

But You may well solve your problems by trying everything else first?
 
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