My audio system consists of the factory head unit, a multi-channel amp, aftermarket component speakers and subwoofer. Every time I push the power button I hear a loud noise - kind of like a “thump” as the system turns on. (It does not however do it when I turn the system off). I’ve also noticed that I get a “buzz” sound through my speakers just before and during a cell phone call. I know the system was grounded when originally installed but I’m wondering if a connection has come loose, or if it could be something else like my amp going bad etc.???
Are you saying when you hit the power button for the head unit, you hear a thump?
Do you know if your aftermarket amp is connected to a hot lead running from the head unit, or one switched by the ignition?
What I think is happening, is that your amp is on when your head unit turns on, and the head unit is putting out a thump (quite common), which in turn is amplified and sent through the speakers. The solution is to connect the remote-out of the head unit to the remote-on input of the amp, which will have the amp only turn on when the head unit is powered up. The remote-out on the head unit should be delayed just enough so that the amp turns on after the head unit powers itself up (and emits the thump).
Alternatively, if the amp is already being turned on directly from the head unit, or if the OEM headunit doesn't have remote-out (I forget), then you just need to introduce a delay, so that the amp will delay a second or so, before powering on. That should fix your 'thump'.
As for your interference near cell-phone calls... That sounds like a poor shielding issue. Are you using exclusively shielded cable to make the runs between components? Think about the difference between an antenna and a length of wire - there is none, which is why interface cables are often shielded. You may be able to replace an unshielded cable with one less-prone to interference, but then again it's entirely possible that it is one of the components themselves that is picking up the signal, in which case you're likely out of luck..
-Josh
