Channel bleed, Cross-talk on small 4 channel amp

[rbsmith2000]

I haveone last problem with installing a small 4 channel amp under the dash to go with a cd changer upgrade on my 2008.

I have a significant cross-talk on the amp, probably from an intra-amp channel-bleed problem. When testing the balance and fader, any time only one speaker is selected (example: Front/left) there is residual music coming out of the other three. This even happens if only one input is plugged in. The speaker wiring is the standard stuff that came with the base stereo. Is there any chance this can be fixed with revised grounding? There is no alternator whine or amp pop, just the unstoppable channel bleed. The amp is just stuck to plastic components, it is not bolted to metal. Only the negative wire is grounded. Would grounding the RCAs to each other and the frame help this?

I've looked through the FAQs and searched (well, everywhere), and folks mention cross-talk, but never any significant discussion.