FM bleeding through CD and AUX modes

Has anyone experienced a head unit's FM audio bleed through the speakers when playing a CD or when running in AUX mode?  If so, what was the cause and resolution?

This is happening to an old but high quality Panasonic DFX99 HU that has been sitting in a garage for a few years, and I'm trying to determine if it's some weird grounding problem or if the HU is toast.  This FM bleed through occurs both when vehicle motor is running and off, but when motor is running I'm also getting alternator whine.  Both the HU and external amp are grounded at the same location, a nice shiny piece of vehicle frame that I ground down with a dremel tool and bolted down very tightly.  The amp is running normally.

Correct me if I'm wrong, but aren't the different modes of operation (tuner/CD/Aux) on separate circuits such that there's no way this could happen unless something was wrong with the HU?

After reading the ground sticky, I realized I did not bother grounding the HU external chasis to anything.  In particular, the bolt with nut in back of HU is not being used for anything, while in a previous vehicle it was used with an L-shaped metal bracket to hold it in place. Could this be a factor?

But if there is no possible way ANY ground issues would cause FM to bleed through, then I'll admit defeat and have to blow more cash on what was supposed to be a budget upgrade :(

It would be easy enough to ground the unit and test. Then you'll know and can move forward.

I won't have time to pull the HU from dash until this weekend, but last night I made two changes that I thought wouldn't make a difference:

1. switched the external amp from high pass to full range

2. lowered the balanced line transmitter input. If input range is 1-5, it was initially on 2 and I lowered it to 1. So it was not a big change (amp input level is lowered all the way).

The FM bleeding and alternator whine dissapeared.  Weird, no? I then upped the BLT input and got a hint of line noise but was no where near as bad as it was initially.  So it turns out there's something wrong with the high pass circuit on the amp, and I also believe something was wrong with the BLT until I played with the input dials.

I later pressed my ear up to the door speakers and could still detect the faintest FM signal bleeding through as well as a hint of line noise, but when seated behind the wheel I honestly cannot hear any trace of noise.  But this weekend I will try to eliminate the remaining noise because while I can't hear it, I know it's there, and that bugs the hell out of me!  I'll try regrounding the HU and test for RCA issues, and I'll also remove the BLT from the equation to see if that solves it.  Wish me luck, and thanks for your help.

Are you certain it's FM?  AM I find much easier to believe...

Regardless it sounds like you have a number of level mismatches in your system.  How did you set all your gains?

HU volume ranges from 0 - 40

I definitely heard 94.5 "The Buzz" Houston FM station.  Initially it was bleeding through to where I could hear it up to about volume level 8 at which point the CD drowned out the FM station.

After the "fix" above I can only hear the bleed through at HU volume level 0 - 1 and that's only when my ear is planted next to the door speaker... it's that faint.  And to be honest I can't tell what station it is now.  It's so faint that it's not worth spending another $350 for a new HU over.

The setup is a Panasonic DFX99 HU (5V preamp outs), soundstream BLT, soundstream ref 700s... all old stuff.  Currently all gains are minimized, which actually matches the HU quite well because at HU volume level 30 (75%) it's getting too loud for continuous listening, and at level 35 (88%) it's rediculously loud with signs of speaker distortion.  The speakers are rated for 60w peak while the amp can deliver ~125w peak to each speaker. So I have to be careful.  At this point I feel there is no need to increase the BLT or amp input levels from their minimizd positions, but I will remove the BLT and run unbalanced cables to the amp to see if it makes a difference (of course then I may have to adjust amp input levels).