I am trying to figure out a "chatter" noise. It sounds similar to rocker chatter but when I removed the belt and started it, the noise went away. I have replaced the alternator (was original 150K miles) and the belt tensioner. I am not sure what to change next. The water pump was replaced about a year and half ago. Could it be the fan clutch?

Sure its not the belt? I've had them make a pitter patter noise- spray some water on it as it is running- see if it goes away......

I spayed some water on the belt but the noise continued.

Don't overlook the steering pump.

I removed the idler pulley and found a few missing ball bearings. Replaced the idler pulley and all is quiet again. :iceslolan