Hissing Noise After New Hu Installation

[Brayden Giampaolo123]

Hi everyone, I have a 1998 ES300. Just had a new jvc head unit installed but now there is a hissing noise coming from the speakers. I've been doing some research and I think it's because they didn't bypass the factory amp, but I'm not 100% sure. Anybody else have similar problems?

[BoaR]

ground loop fault.

do a search.