Engine Rattle

I have a 1998 Rav 4 with 151,000 miles,shortly after starting(after several hours setting)
the engine rattles like hell for about 4 minutes then stops.Does not do it until after about of a minute of running.Sounds like it may be coming from the lower right front,around the a/c compressor,but does not change with air on or off.Any ideas?

This is not my area of knowledge by a long shot, but I've seen other trucks do this kind of erratic thing when the ECM is faulty. Just a wild stab in the dark.

what engine?

Water pump So I would change the t belt and water pump or just don't drive far from home!