Originally Posted by hangflyer
The noise can only be described as a white noise, no distinct pitch or tone, no relation to engine RPM except that it appears and disappears within 50rpm of 2200rpm every time. There is a chop to it, but it does not change with RPMs.
Might be a clue - can you describe the chop? Frequency, depth, m/s ratio? Any chance of recording it and doing some lab analysis with a scope or spectrum analyser?