Originally Posted by jonywalker
Hiss is such noise signal comprising high frequency components, your subs normally are not able to play that noise. I assume you made a wrong grounding. This is the case e.g. the amp is grounded onto the (-) bolt of the battery, thus inducing the low frequency noise from the electric generator into your amp.
i used to ground it here (1st pic), new ground location (2nd pic) to shorten the ground cable because i placed my amp on top of the oem amp