Hi, I'm new here & feeling my way around. I have a '94 Mustang Cobra that I've had for nearly 20 years. It has about 71,000 miles on it & runs great. It is still pretty much bone stock. The 460 Mach 1 radio was (and I mean WAS) the best sound system I had ever heard. About a year ago, I noticed a hummmmm coming from the radio & I can tell it is caused by the engine running & can tell that it is the firing of the spark plugs because it hummmms faster the faster the engine is revving. The radio sounds perfectly when the car is not running. To make matters worse, it doesn't do it all the time when it is running & the pattern is unpredictable. This has been going on for over a year now (off & on). One guy said he thought it had something to do with the fuel pump & would need to drop the gas tank to find out. I'd rather not go through that until I have more assurance of what the problem is. It's starting to drive me nuts. Any ideas? Thanks.

 

I'd guess a loose ground somewhere or a shielded cable has a breach in the shielding.