Hi all. I've been revisited by an ongoing mystery since I purchased my '95 E36 M3. When the engine is warm, under light throttle, at about 1600 RPM, there is a very noticable 'growling' noise coming from the engine. ONLY at that engine speed. Hard throttle, you don't hear it, rpm's go by too fast;^) My mechanic took a stethoscope to the valve cover and found the noise to be coming from the cam sprockets, or that area, at least. He could even put his fingers on the valve cover and feel a vibration when the engine was at that speed. First, he thought the hydraulic chain tensioner went bad. Replaced it, didn't stop the noise. Called a buddy of his at a dealership, said he's heard of this problem. Was told the bad tensioner was coming to a resting state too soon, allowed too much slop in timing chain. Soooo... Replaced timing chain, and both cam sprockets. Noise wasn't completely gone, but much much better. A few months later.... Fast forward to the present. It snuck up on me, but the noise is back!! No oil smoke, no puddles, no oil stains on the engine, no red lights on the dash, computer not complaining about it, no stalling or couging from the engine. Plenty of oil. Motor runs very strong. What could it be??? Could the oil pump be going bad? Could it be starving the engine at that speed? Any advice would be appreciated. Sorry for the long lenght of this message.
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