hey......i dont really know very much about these setups....i dint even install my own...my friend did most of it.....i THOUGHT he knew wat he was doing...anyways....i have a crapy eight inch sub in my car...no amp (dont worry i have a clarion system en route...) anyways i cant figure out wats wrong....it has an internal amp.....the problem is when i turn the sub up in my trunk it satrts to make this rapid thumping sound and it gradually gets slower as i turn it down...WHAT IS GOIN ON!!! please help...i appreciate it