I tried my Amp9 in my car for the first time last night, and I've been getting some wicked noise coming from it when the engine is running. It's a whistling in tune with the engine speed and it's *loud*.
I tried installing a noise filter (rated 15A) in front of the amp; no difference.
Using a regular Kenwood car amp, there is no noise, so I know the signal from the head unit is clean..
I tried grounding and ungrounding the RCAs directly to the case.. no difference.