Audiovox CDM-8940

Ok Maybe one of you guys can help me out here, I got my 8940 like 3 days ago, have skimmed the manual and am still trying to figure somethin out. When i was looking at the phone in the vedrizon store, i was looking at one of the ringtones and played it, it was some rap or r&b song that every couple of seconds while it was playing, the phone would vibrate as if the bass was hitting or whatnot, maybe its only on certain ring tones or w/e, but any response would be greatly appreciated.