I'm a Volvo tech and I bought a '90 740GLE with a 16 valve engine. When I got it it had an oil pump pulley that had broken off of its shaft. Both the pulley and the shaft showed signs of wear, so they no longer were a tight fit where the pulley slid over the shaft. I had the head fixed, and changed the oil pump, pulley, all the idler pulleys etc. and got the car running with proper belt tension. And I changed the oil pressure relief valve, which came with the new oil pump. The problem I have now is that I keep getting this buzzing sound on the left side of the engine, accompanied by a drop in oil pressure. When it first happened, I saw the oil light flickering, so I put a gauge on it and sure enough, it had low pressure. It could possibly be in the left balance shaft, but I'm hoping that somebody out there has run into this before and might be able to help me out here. If you think you know whats happening here, I'm sure open to hearing it!