When you say "high volume", what do you mean? When you turn up the gain? (you said you unhooked the RCA from the MS8; so I'm just looking for clarification)

You have, by pulling the RCA, eliminated the MS8. Ideally, put shorting plugs on the amp's RCA inputs to keep any external noise from coming in through them. Try swapping the tweeters to opposite channels and see what the noise does; this will help determine if the amp has issues or if the speaker wire/passive crossover is picking up RFI from something nearby in the car.

 

I got to more troubleshooting the other day...findings:
The noise does not switch sides
there is no passive crossover, so it cant be the crossover...theyre ran active. I never got around to putting capacitors on them, so i sure hope theyre not blown. The speaker wires go down each side of the car, through the boot and into the door. Could the amp be blown? Its a 450/4 so those two channels have their own power supply

 

Do you have a spare mid/coax laying around and can you get at the wires, you could hook that up and see if it makes noise you would know its the amp/wiring. Which I suspect since the tweeter would make no sound with no signal, unless the wiring was shorting or amp is getting interference. Anyway a mid/etc is not going to get blown up by crackles while you trace it down. You could run a wire and speaker off the amp direct to test car wires.

 

I was thinking about running a wire directly from the amp to the tweeter outside the car, this way i could see if theres interference . The coaxial is a better idea for the sake of blowing the tweeter while troubleshooting. I have a old kenwood 6x8 laying around ill hook it up directly and post results. Should I try reconfiguring the ms-8? Ive considered that may be the problem, it may have forgot a setting or something.

Also I should add in that I believe I recall there being a pop before the tweeters began to have this problem. Im not sure if that helps anyone with a diagnosis

 

The tweeter might be toast, but it still should not make sound without power from the amp. Even if the VC is toast it needs power to move and make noise. I would suspect the amp has a problem or is getting a signal to do that. I always run a cap on tweeters active to protect them, an amp pop can trash them. I guess I would try some other speaker and see if it plays, pops, whatever. Sure check your settings before tearing into stuff.

 

If you swapped speaker wires, and the noise stayed on the same tweet, then the noise is either being picked by the speaker wire or the tweet itself.

 

i assumed that too, but dont know where it could be coming from..theyve always been fine so i dont see why they suddenly would be picking up noise