I turn on my woofer/amp setup with no music on and the woofer still vibrates and sometimes beats. I know the problem is EMI, but I can't figure out what to do about it. Has anybody else had the same experience?
I could write a book on noise. Check your grounds first. Make sure the sub amp is grounded properly and make sure the head unit is also grounded properly. In theory these should yield the same resistance for a noise free system. Make sure your RCA cables are not running by any power cables. If it's not these two we'll dig in deeper.
I doubt it's because your ground is too long. You could have a "ground loop" problem. That's when there is too much resistance along the ground path between the signal source (head unit) and the amplifier. Usually, good grounds at each location will resolve the problem. However, sometimes there just isn't a good path for the ground to travel through the body/frame of the car.
The cheap solution is to run a small wire (18ga is plenty) from the ground wire on the head unit to the ground connector on the amp. Many RCA cables have this small wire in between the two coaxial leads, so you don't have to run a seprate wire. Accordingly, many amps have a small screw right above the RCA inputs, specifically for this secondary ground connection.
If you don't feel like running another wire from the head unit to the amp, you can purchase a Ground Loop Isolator from Radio Shack. It plugs in-line with your RCA cables, and it resolves most ground loop problems.
Um, the stereo ground? If that I have no idea where it goes. It's just the stock ground installed by ford. As for my amp ground, It's secured under a bolt on the right wheel well in the trunk. I've heard a rumor that seperately wraping all of your wires in tinfoil would help. Any truth to that?
I have never heard anyone using that method. What I would do personally is get some self tapping metal screws, Or drywall screws work great, pick another area and just sand the hell out of it, brush it off (until the metal is very shiny) brush it off, and try grounding it there. Otherwise your probably looking at a hardware issue with either your deck or your amp.