Well actually, i KNOW from personal experience, that in my commodore (yes its not an sr) the big end bearings went on that, and before the motor died it made a knocking sound as you increased the revs and especially under load with the sound getting greater at heavier throttle. So yes, you do hear it at a certain rpm before the motor dies of course. The big end bearings can set your motors life short instantly, over very short time or could extend over a longer period of time depending on the severity of the damage to the bearings.