I just recently heard a heart beat type sound comming from my subwoofers in the back on my truck. I don't know what caused it, but its wierd it only starts after I start the truck or when its not in idle. I rev the engine and it is magically gone..... If any sound system buffs can help me out or maybe its just some pertruding sound coming from my fuel pump that may be pusating the gas through the lines???? Please and thanks for any information given!!!!!

 

Could be a ground loop, or it could be that your amp/speakers is getting too low of a voltage at idle. Test at your battery with the engine off, and then with it at idle. You should have about 12.5 volts or so with the engine off and about 13.5 or so with it at idle. (Give or take) if it is significantly higher or lower at idle, it could be the power supply in your Amp or head unit that is causing a voltage spike to be sent to your speakers.
Also make sure that the polarity on EVERYTHING is correct. Make sure that the + and - speaker connections are right, and connected.

You are getting a voltage spike somewhere, I would be willing to be a speaker wire someplace is reversed, throwing the whole system out of phase.

MK

 

Sorry, also it could be that you have a bad sparkplug/coil. This could be arcing and it is being picked up by your headunit/amp.
You can try a line filter inbetween your battery/amp/headunit if all other tests are negative...
MK