I have a question for my audio expert friends out there as I am completely stumped.

I have a 2002 BMW M5. It was originally DSP, but using the helpful directions from members here I removed the DSP amp, added in the additional 2 channels of RCA's, and started using an aftermarket 4 channel amp to power my components in the interior.

Everything works absolutely terrific, and I am thrilled with the results, but always intended to add some bass - so I added a 2nd amp this week and it didn't work.

Here is the issue: I have 4 channels of RCA output that work great when attached to a single amp, but do not work if split between 2 amps or if used with pass through RCA's to a 2nd amp when the tuner is powered on.

Trials:

• When I hook up the single 4 channel amp, everything works great.
• When I then use the pass through RCA's to the sub amp, I get horrible noises that are constant volume and do not change with the volume control. It sounds like terrible whining, even when the engine is not on.
• If I only use 1 set (front or rear) of RCA's w/ the 4 channel and the passthrough to the sub amp then everything works fine.
• If I split the 4 channels from the tuner and attach 2 to the 4 channel and 2 to the sub amp then I get the nasty noise again.
• Strange: If the amps are powered on before the pass through RCA's are connected, then everything works fine.
• Strange: If the amps are powered on with the RCA pass throughs connected (resulting in the nasty noise) and the RCA's are then unplugged then normal sound returns even if the RCA's are reconnected.
• If I provide a 2 channel signal from a different source (Ipod) to the either amp, or to the 4 channel with pass throughs to the 2nd amp then everything is fine.
• Reseting the amps (by pulling the remote turn on wire) has no effect - the entire vehicle (ie. tuner) must be cycled.

I cannot for the life of me figure out why the tuner provides a signal fine when attached to a single amp, but fails when attached to 2 amps in any way at the time the tuner is powered on.

I've already checked the ground and it measures 0.0 ohms from ground point to battery negative (yes, really - wire brushes on a power drill do a terrific job of removing paint!).

Clearly everything points toward a bad tuner, but since it worked marvelously before the upgrade to remove DSP, I hesitant to replace it...

Any help is greatly appreciated!!!

Doug