iv installed my dbaudio sub into my a4 iv used the high level input into the amp, by using scotch locks to get feeds from the right hand rear speaker. now the sub and amp worked fine in my old car but i had phono leads from the stero. i want to try and use the standard stero which is a sympthy cd\tape deck, sorry for babbling on ill get to the point when setting the sub up i got it sounding really nice and was chuffed, but when i turned off the engine there was the was a really loud rumble that came from the sub. the same when i turned it back on. now if i turn the gain down on the amp it goes,iv checked all the earthin points and thats fine. what could it be???