you dont want one of them 1s u poasted you need one of these
http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&TabID=1&source=14&doy=15m2
all you need is one between the hu and sub amp in the rca line
if you get a good eqauliser you might not need it as the better equalisers have ground loop isolation circuits built in.
normaiily the cause of a ground loop is due to not having a good enough earth either between the amp and the bodywork or the battery and the body work
basically the earth on the bravo/a between the battery / body is 4gague for the whole cars electronics!
so if u run a 0 gague posative lead from the battery to the amp you are only geting the benefit of 4gague because of the negative! also minus what ever the car is using so lets say 6gague worth of current flow for the earth.
now when you shove all that posative power down to the amp, when it comes out the amps nagative terminal it has no way of geting out quick enough, so it goes and finds another negative path which will be your rca cable to your headunit! now the power runing up the cable causes a feed back loop which comes out as a whine which changes pitch with the engine.
a ground loop isolator stops this by breaking the circuit in the rca lead! but i does not really cure the main problem that you dont have a good enough earth!
