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Hi all! I have an 07 Mazda3 which has the BOSE head unit. I recently pulled the BOSE amp and sub out, and replaced it with aftermarket components. The new amp I am using is a Alpine MRV-F540. I replaced the BOSE speakers with 6X8 Alpine SPR68's. I then tapped the high level inputs under the driver's seat and used speaker to RCA wire to convert the signal to low level for use in my amp.

I am having an issue with system hiss (White Noise) which I cannot get rid of. The noise is not loud to the extreme, but is clearly present and intrudes on the listening experience in my ride. The noise becomes louder as I turn my gain and volume up. When no signal is being sent to the amp (IE, my HU muting the signal between switching tracks), the noise completely disappears. It is present, in some form, no matter how I have my gain set. If I lower it all the way, I need to turn my volume much higher on the stereo which results in the noise reappearing with the same intensity as I turn the volume back up to my normal listening level (And it sounds crappy at low gain levels).

Through much trial and error over the course of 3 months (tried too many things to list here), I have determined that the noise is originating from the Head Unit's output signal in some form; It is NOT related to my ground, wiring, gain setup or a defective amp. Short of switching out the head unit (Which I don't want to do because I wish to retain my factory controls and display) what other options do I have to fix this?

One thing I have researched, and the only option I saw which may work, is getting a line driver with balanced inputs. I looked all over the web, and I saw conflicting information on whether the more expensive line drivers with balanced inputs will effectively reduce "White noise" or not. I briefly looked into a JL Cleansweep but it's equalization, I've read, will have no effect on my setup since the BOSE head unit outputs a line level, unmodified signal and the equalization is the only difference between the Cleansweep and other line drivers with balanced inputs (Correct me if I'm wrong).

There MUST be something I can do!!! I am no audiophile, but I want clean sound without all that hissing garbage in the background. I've brought my car to a tech, and he said the noise was an unavoidable consequence of the stock BOSE HU. I refuse to believe that, since I was able to max the gain on this same amplifier with an aftermarket HU with NO NOISE! If anyone can help, I would be extremely appreciative...Thank you!!!
 

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Did you ever figure out your problem?
I am having a similar issue. My tweeters hiss and go up with my gain but stay the same with my volume, which is the same level hiss with the HU off.
 
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