I've had my system in for 2 years with no problems. I have a JVC head unit, preamp out to a MTX Thunderform. It's been quiet up until now. I can hear engine noise whenever it's on. I haven't changed any stereo stuff, but I have been working on the engine. Can I be getting more noise now because of something I did under the hood? What about an arcing spark plug wire? I don't know where to begin.

 

I think I know what you're talking about... a whine in the speakers that corrilates with the engine RPM.
This is usually caused by a loose connection somewhere in the stereo system... alot of times it's the antenna plug on the back of the head unit.
But check all the connections, especially the power and ground wires.

 

This engine work you did, did you change plugs and/or plug wires? If so, and they are not the right type, this could be a cause of engine noise in your stereo system.

 

A change in wiring any where in your car can cause this type of engine noise in your system. It can also be a loose connection in your system's wiring. A higher powered alternator can do this too. Just go over everything youve done to your car recently.

 

I have solved the problem. I think I had a spark plug wire that was broken internally, and the arcing was causing the buzzing in my sub. I replaced my wires and the noise is gone and the car runs a lot better!