At idle...loud noise from engine compartment on 2000 Toyota Celica

2000, 2ZZ motor, 150k mileage, Inconsistent engine noise at idle. Sometimes it makes noise sometimes it don't. Noise sounds like a wrist pin rattling. Is this something common? Like a timing belt pulley bearing??? Help.

Asked by for the 2000 Toyota Celica
The Celica GTS with the 2ZZ engine has a fan belt with an automatic tensioner, to eliminate any possibility of a problem there I would remove the drive belt and see if the noise is still there. I have seen them give problems. Check of course the engine oil level. Listen and see if the noise could be from the timing chain area. Also ensure the noise isn't related to the air conditioning compressor, get some one to cycle the air conditioning compressor on and off while you listen see if the noise happens each time the a/c is turned on and off.