I had a 98 chevy pick up once. Intake manifold gasket was poo-poo. Looked like baby crap or peanut butter and syrup was in the oil. Replaced the intake manifold gasket, and didnt last 2 more weeks before the frikkin engine was about to spin a bearing. You could hear it smack and chirp against the crank. Never did scar enough to lock it up, but I stopped driving it. And it eventually went to the highest bidding junkyard with a value of $200. Nice straight body too. I should have just gotten another engine for it but didnt have the money. Plus it had transmission problems. Its random, but thought I would share my experience with an intake manifold gasket problem. FYI it was running fine. I didnt dog it or anything, was driving 50mph and all the sudden it began to smack and chirp. I could have cried.