Get a few feet of small diameter hose, put one end up to / into your ear canal, move the other end around the engine until you isolate the source of the noise.

Check the o-rings on the oil filter center tube - there are two small o-rings at the bottom, if left too long they get hard as a rock. If they degrade too much, strange noises can result. I can't explain why, but one poster just about went crazy trying to figure out a weird noise and replacing those o-rings fixed the noise.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC