So in my car, i have diamond m5 audio speakers, powered by a 4 channel soundgate amp.
I got the amp tested, its fine, the headunit is fine, i had the whole system completely reinstalled and grounds all relocated, and they still whine super loud with the rpms.

I tried it with a different amp and headunit and it still did it.
The guy at the shop said the only thing he can think of left to try is the alternator or battery.
What do you guys think it could be?

 

you need a bigger alternator or just to put a dry cell battery in your trunk and you wont hear it anymore

 

Where do you hook up the dry cell battery for power?