Driving about 40mph in 1997 Ford Explorer 4x4, 120k milage, going on the flat, not much load on the engine, not in fourwheel drive. Sudden ZZZZZing noise, very loud, then stops. Happened four times over the course of 20 mins or so of driving. No discernible change in engine speed or vehicle speed...Transmission? Sounded almost like the starter motor spooling up at a very fast speed and then disengaging? All the belts and fluids seem fine. Drove about 300 miles subsequently and noise has not repeated since.
Only thing that comes to mind with description is maybe heat shield on exhaust, getting loose. Wait until vehicle is cooled off and get under there & check any heat shields you see wrapped around or near exhaust, above it attached to floor of vehicle etc, and give them all a little shake or rap with rubber hammer or similar to see if any rattles are present.
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Worth checking out, and I will. Thanks! It's hard to describe the sound in words, it wasn't a rattle, it was more like a zzzZZZZZZING...then repeating later a couple times. Sort of sounded like somthing "winding up" (or a part of the transmission? 4 wheel drive? some kind of motor kicking in perhaps as a result of a short that is not supposed to kick in like the starter all of sudden kicking in? From under front of car. Anyway, thanks for your comments.
Don (original poster)
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