Re: Ground questions.... Any negative effects with ground loop isolator ?
A ground loop isolator is a tool used to help you determine where your ground loop is, they are not a permanent fix.
Since hooking up the isolator to the RCA coming off your head unit to your amp made the noise stop, that means your head unit is the source of your noise.
Since your head unit is a pioneer it is likely that you need to ground your RCAs to the chassis. Also using a different ground then the factor one from the harness won't hurt either, even using your own power wire might not be a bad idea if the noise still won't go away.
References : chaunb3400, Team H&K, diminishedpower, pickup1, sublime06, sporty_drew, JRock10, Jando86, sundownz