It depends. If the sound is a sharp "Tink!" that only happens when you step on the gas from a standstill then it could be a universal joint getting loose. The universal joint is a connection between the drive shaft and your rear end. No not your rear end, that would be silly. The rear end of your expedition where it goes into the rear axle. I would get it looked at as soon as possible.
You blow into the Flute's mouth, The sound comes out the rear end.
There are many sounds it can make, but it's the smell you need to worry about!
To the end of your drive.
Depends on the sound - if it changes frequency pitch when you speed up or slow down, then it's likely the main rear-end bearing wearing out. It sound like a steady whine - the key is whether the sound changes when you speed up/slow down, telling you it's a rear end problem. Brake sounds would only be heard during braking, etc. The other likely cause is in the same area, and that's an axle bearing wearing out. Same sound as a differential (rear-end) bearing going bad, but less volume.
Any brand of WD40 oil will work.
the axle is a shaft that goes into your rear end from one side with the wheel bolts on it and the other connecting into you rear end differential gears.
75W90
75w90
Loud, whining, growling sound. Rear end jerks at random if bearings are locking up.
I had the same problem. The bearings in the swing arm were worn out. This caused slack in the rear end and a misalignment in the u-joint on the drive shaft and made a popping noise.
rear wheel bearings are bad