Stumped and frustrated

So I finally replaced a shitty 5 channel amp and eq. I had a taco tunes 5 channel amp and Recurve EQ. For reference I have a 2017 4Runner with image dynamics component set.

When I got this installed about 5 years ago I immediately had the following issues;
- static pop noise when turning car on
- ground noise out of right tweeter (would get louder when reving)
- bass non functional

I finally took it back in to another shop to get everything clear up. I had my doors deadened, installed pioneer GM-DX975 and Audio control lc7i pro.

Everything is great except I am still having ground noise. When I have the radio of you can hear a slight buzz/hiss still.

The shop said this is typical as the speakers aren’t receiving a signal. I found this hard to believe but I wasn’t quite sure what to say as this is not my expertise. I thought it was a ground issue or maybe a gain but the installer didn’t agree.

I’m happy with everything except this. The component set REALLY came alive with this new amp and it sounds great but want to get this last piece fixed. Any suggestions? I’m new to car audio as well.

Thanks

Bump. Feedback welcome

Bad grounding can indeed cause noise. But, I’d suggest checking if the AccuBASS and other features are correctly set, and that the input gain isn't too high.
Also, low-quality or damaged RCA cables can cause noise.
Make sure the wires between your head unit and amp are good. Look for any bends or cuts in the wires or anything that might mess with the signal.
If you hear a high-pitched hissing sound, it might be from your car's alternator. That's a common problem in car audio, but you can fix it by adding a special filter for that noise.
You could try ground loop isolators if nothing else works, though they might affect sound quality.