engine whine is a ground loop, running power lines with rca's won't cause it unless running garbage (a guy who won sq finals in iasca proved that theory wrong a while ago as he had everything in a bundle to prove it) a cap can help as that is basically what a ground loop isolator is (just hook it up on the ground instead of the power) I always grounded mine together (used a distribution block even on the competition vehicles, and was the preferred method at the time) keep the grounds short as they can act as an antenna
