I would have him pull it and check the indexing (mesh) on the gears. A whine like that, that stops with a load change (accell/decell) point to an improper indexing, or "backlash".

Jeff!
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Original Registration, NOV '07
Pre-crash post count - 396

"...the Earth will continue turnning, even when justice dies." (Revy Two Hand, Black Lagoon)