You may not believe this and some may even say im full of Bovine Excrement but I have had this issue occur with some aftermarket oil filters on Chevy V-8's. Try a AC Delco filter if you are not already using one. What you hear is the clearance between the rod bearing and the crankshaft until the oil film fills the space. A lot of newer Chevys make that noise and the dreaded piston slap as well. It seems to me car manufacturers anymore are making engines on the loose side for better fuel economy.
