it could just be the oil sender is faulty and not reading right(not that the stock guage is worth two poos, get an autometer). the noise could be a faulty tensioner pully or something. at idle it can hold but then at faster rpm it can spin on the bolt instead of the pulley spinning like it should therefor making the belt make a "fwap fwap fwap" noise as it tightens and loosens(the pulley bolt being off center and the entire assembly spinning around). if you are knocking way loud though, it might be the engine. it may just be a coincidence that it is making the sound near the timing belt area. when is the last time you messed with the timing stuff?

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