Subwoofer randomly thumping

[technophreak]

Here is my dilemma. I have a subwoofer that randomly thumps pretty hard whether i'm running from the battery or if the car is started. But only if the car is started does it constantly vibrate as if it was timed to the engine. When I turn the engine off and let it run from battery, the vibration stops and appears to operate normally aside from the random thumps that happen. And if I use it for a while, the vibrations go away and at times will not be there at all when I first start the car.I have tried different ground points, power cables, RCA's... I just find it strange that its constantly vibrating when the engine is on. Any suggestions on this one?

[idontknowwhatimdoing]

It sounds like you are suffering from "motorboating" which is usually a ground loop problem. Check also the actual power from the battery and all connections. You might even beef up the ground from the battery to the chassis. To test, take a jumper wire and ground one side to the amplifier's ground and the other side directly to the negative terminal on the battery. If it goes away, then you have a ground loop to get rid of. Jahtassa may have some other advice for you as well. Good luck, noise can be really frustrating.

[idontknowwhatimdoing]

Also motorboating is usually a result of using power wires that are too small for the amp, a ground wire that is smaller than the power wire, or a low voltage potential on your ground. What you can do is check your voltage across the battery terminals with your car off. Now connect your positive terminal to the positive lead on your meter and your negative lead to the spot you grounded your amp. Chances are the voltage will be very different. With newer cars like the Vibe the trunk area is attached to the rest of the chassis with weld paste, This weld paste has a fairly high resistance. If this is the case you can use the same method above to find a good ground (no voltage drop).

[Jahntassa]

What kind of amp? What's it rated at? (Or even better, what's the rating on the fuses?) What size power wire do you have?It does sound like it's something to do with the amp, whether it's a bum connection, the power wire isn't enough, etc..we'd have to figure out.. It could be an overly sensitive amp!Also, are you running the factory or an aftermarket radio?

[northvibe]

what about the remote wire from the deck to the amp? idk how much that would deal with it, but i know it turns the amp on/off when car is on/off. I would forsure check the connections on the amp like idontknowwhatimdoing and jahntassa said.