'00 F350 hum at 2200 rpm
Hi - this is my first post on this great site!
I recently bought a '00 F350 7.3L automatic with 96K miles. Runs perfect, drives perfect. Except for a hum. The hum seems to come from the front of the truck.
The hum comes around 2200 rpm. It's there at 65mph (in overdrive, or 4th gear). When I go up to 75 or 80 mph it goes away.
2200 rpm is slightly above where it normally shifts through each of the gears. But if I hold it down in 1st gear, the hum comes at 2200 rpm. Same if I hold it in 2nd gear, or 3rd gear. So it's related to the rpm, not the speed of the truck or gear it's in. (I did try running up the engine to 2200 rpm in "park" and did not hear anything. It seems like the engine needs to be under load to make it hum.)
If I'm going 65 mph, and it's humming, then I drop it into neutral, the engine goes to idle and the hum goes away - even though the truck is still going 65mph down the road. Therefore it's not tire noise, though it sounds exactly like tire noise. It's not bearings or the drive shaft (right?).
My mechanic thinks it's something resonating but is stumped.
I've seen others ask the exact same question on here (and other forums) but no answers. Hoping someone has figured this out!
Thanks for your help!