You'll first need to eliminate the simple things. Check the tightness of the belt as well as the condition. Usually this would cause a squeaking noise, but I've seen/heard stranger. If this isn't the source of your noise, remove the belt and turn all of your pulleys by hand. (Try to turn them fast) If one/more of them are hard to turn and/or make any noise, that'll be the problem.
If all pulleys check out good, purchase an automotive stethoscope and use it to listen to various spots around the engine. However, this'll mean removing parts of the engine once you've located the source if it turns out to be internal. If you need a specific procedure, let me know.
Monday, February 14th, 2011 AT 1:24 AM