Weird Engine sounds

Hey, guys.. i have this sound comen from my belt area..i donno if its a pulley, i was told that if the belt is moving from side to side, then it would be a pulley..but its not doing that .. the sound is almost a crunching sound, but its not coming from the "enigine block area" its comen from teh belts, and the higher the RPM the louder it gets, also the only engine mod i have is Full exhuast and intake......THanks J