Saab 99, 90 (1969 - 1984)
Just done an oil change on my 99, using Valvoline 10W40. On start up there was an erratic knocking/clacking sound coming from within the crankcase, seemingly from the area around no. 3 or 4 piston, that wasn't there prior to the oil change. Noise goes as the revs rise and don't always come back...