When my car loses revs quickly from 3,000 to 1,500 you can hear this sharp "knocking" noise it sounds like, The pistons not catching enough oil, but im certain the car has enough, i had a friend listen to the noise, he said it sounds like the heating wall is banging, nothing engine related. Also i checked the oil and there was no sign of "Burnt paper smell, metal practicals in the oil. So i'm stumped. Any suggestions?