Putting one of those http://www.customautosound.com/ stereos in a '67 Mustang. Its just an am/fm unit. It really picks up the alternator whine. And when you press the brake padal, you can hear that too. The old stereo never did this (when it was working). So I figured I needed a filter. A local stereo store sold me a Peripheral PCF10. If anything, that made it worse. A lot lower tone. I know there are lots of differnt styles of filters out there, which would work the best?
I had the same problem with the SecretAudio in my 66 Fairlane. My problem really was the MSD box. I bought a noise filter from MSD which helped alot but didnt eliminate it. I tried shielding it and grounding it and when I moved the unit farther from the firewall it improved alot. It isn't perfect but I really only hear noise when it is turned down low.
The ignition is all stock. I have a little noise in my Comet with an MSD 6A, but it isnt nearly as bad as this new radio in the Mustang.
if it were me i would move the constant 12v supply to its own circuit, and run new ground to the ch***is, also make sure that the switched ign isnt hacked into a circuit that runs straigh to the engine compartment. are you using a seperate amplifier?
No amp, just an am/fm radio and two speakers. The one they sold me is at the bottom of this page http://peripheralelectronics.com/web/noise_control.asp . Says its a choke filter?
Check for the grounding at the radio, sometimes the factory ground is not that great, also grounding to the dash, sometimes that is not sufficient either, only other thing I can think of is make sure a speaker is not grounding out on either wire, I've had that induce noise once. The connector on the speaker touched metal slightly when the speaker was in the hole.