sounds to me like a wire is touching the body of the car some where or your radio is messed up to make your sub serge like that i would disconect one speak from the amp at a time and see if it works right or dis. them all and hook one up at a time then if it keeps doing it take out the radio and use one speaker((you have just sitting around))then try each channel of the radio to see if there is a problem if nothing again your amp is shut and the inside is fired