Squealing engines...
This question refers to a 747-400, but I think it is relevant for all turbofan engines...
When I watch these aircraft taxi up to the hangar at EGSC, the engines sound very much as you'd expect, but when the HP cocks are cut, the engines emit a very load high pitched squeal as they spool down. This sound is not audible during normal idle conditions, so why does it appear when the fuel is cut? Does it have anything to do with gear trains or something? The intensity of the noise seems higher at the front end of the engine also.
Any engine experts out there who can offer an explination, it's been bugging me for ages!
Nish