Sounds like tire hum but not sure...

[Trueoo7]

Just bought this used (65K) and have only put about 50 miles on it so far, 2003 explorer 4WD V8. I have what sounds like tire hum that you would get from aggressive tires, but their not at all (very tame). Thought it was left front bearing so it was replaced and noise is still there. I've seen where some threads say to check the rear bearings and will do this next. Could this be locked in 4 wheel drive or maybe the hubs. I see it has 4WD Auto but it doesn't feel like its in 4WD. The hum gets noticable around 20mph (real noticable at 40mph) all the way up to 55-60mph and then all the way back down to almost 5mph.
Any thoughts....Thanks

 

[Trueoo7]

OK, no thoughts I guess. To update I brought it back to dealer (under warranty) because rear brake was sticking and after taking it for a test drive, he has decided to replace the transfer case due to this noise. I didn't think the transfer case could cause this type of Wrrrrr but I'm not going to argue if he wants to replace it. He never mentioned the brake so I guess its fixed. Its going to take a few days to fix so we'll see....

 

[DAT05EXPLODER]

i wouldn't complain about a transfer case replacement either. especially if it fixes it.