My friend has an extremely loud knocking noise from the motor of his 1990 Z24 Cavalier 3.1. The car starts alright and it seems to have lots of power. The knock sometimes goes away for a few seconds when I rev the motor to 2000 rpms. Additionally there is about 320 000 km on the car. The motor oil level is fine and the oil pump is circulating the oil.
Any ideas as to what the problem could be?