I am having a similar problem. My current setup does not include an external amplifier, though. It has the empeg running through the AUX in on my CD receiver.

Recently I was having a voltage problem with the empeg, and so I wired the constant power (yellow) line directly to the battery with an inline fuse. Before I had done that, there was still some noise in the system, but it was not audible unless I paused playback on the empeg and turned the volume up on my CD receiver higher than I would ever go.

But now that the empeg is wired directly to the battery, the noise becomes audible at a lower volume on the CD receiver. The CD receiver's AUX in is on the front panel. If i disconnect it, the noise vanishes. Also, when the engine is running, this noise does change pitch with the engine's rev or even the empeg's drives spinning. With the engine off, the noise remains, and still changes pitch with the empeg's drives spinning.

So, knowing that the noise is coming from the empeg, what would be the most likely cause?

• The direct constant power (yellow) line to the battery?
• The sled is not grounded well enough?
• Or something else entirely?