i have tthe boss b-50 and the b-70's on my tower pushed by a rockford fosgate amp. and there is an engine noise in them when the boat is on, i added a ground loop isolator and its still there, what could be my problem?
run a ground and power from the batt to your head unit. Factory grounds and power are all tied in with the gauges and other dash acc. Should help, and also make sure you have solid grounds to the amps.
This is an electrical back feed from not having a proper ground. Most common fixes are listed above. Such as running all audio caring wire (RCA and Speaker wires) ran in a separate location. Make sure that you are using the same gauge ground wire or bigger for your ground wire then your power wire. Also use RCA wire that has a ground apart of it and float (terminate) that ground at the amp only. (Most amps now days have a specific screw for that.) More in likely this issue was cause by the addition of amp but it could possibly be originating from your deck. I would run you deck ground back to the same point as your amp ground and possibly getting a second battery for your stereo with a batter isolator. If the noise continues I would look into to the fact it could be a bad amp.