Still haven’t tracked it down. Rebuilder installed a new dipstick tube and thought it might be vibrating and rattling. But no. Sound is kind of like ball bearings rattling in a can. Not quite though. First few miles of driving cold this morning it wasn’t there but returned once warm.
93 GMC 2500 pickup
4WD Xtra cab.
New Optimizer 10/14
Rebuilt Central Plains Diesel IP 10/14