Sigh. Technic changed the harness in the last production run to male RCA. I thought they were getting a little longer but no such luck.
The stock amp is relatively flat from around 3K to 20K, so it *ought* to play any hiss present without attenuation:
But you also pulled the foam out from in front of the tweeters, yes? The stock tweeters would have louder hiss now as well, wouldn't they?
Did you say on the phone that one side was louder than the other? If you swap the RCA, does it move?
I'm worried that it's the HU too. Have not run into this before...