Squeak at low rpm?

[mrian]

I have been trying to pin down a squaking sound for a while. I have a 2.7 2003 base model, and at low rpm and under torque load (pressing on the throttle in a higher than ideal gear, for instance, 5th gear at 35mph), a squeaking can be heard from the right side of the engine, presumably through the radiator hole on the passenger side. The squeak increases in with rpm up to around 3000 rpm, when it is not audible anymore. My suspicions led me to a water pump pulley being loose, and grinding into the pump housing, but this didn't fix the problem, as it came back. This time, no loose water pumps are to blame. Does anyone have any ideas or experience of what to check? Any theories would be appreciated!