Oh, where do I start? Transfer Case?

OK, this started happening last night, I haven't had a chance to look at it, but I'd like some tips on where to start looking.....

You ever accidently leave your truck in 4wd and drive around? Me neither, but I have a "freind" that has done it. Anyway, you know that whinning sound that the front end makes when your in 4wd? My front end is whinning like that all the time in 2HI. I also noticed a slight shutter when comming to a stop. I made sure that it wasn't in 4wd. I have the manual transfer case, and I cycled it from 4HI, 2HI, N, 4LO a few times, but it seems to have no effect on the noise in 2HI. Another weird thing I noticed. If I'm driving at 60 mph, and lightly apply the brakes, there is a slight rumble, only if I'm going straight. If I'm on a curve there's no rumble. Weird eh?

I don't know why, but it just seems like I'm in some sort of half-assed 4wd.

Any ideas? I appreciate the help

Thanks guys

5.3L 1500 4wd (manual transfer case)

Could be a couple of reasons for this. a) Type of tires and possible allignmet issue, b) Bad front wheel bearing, c) front differential acuator motor malfunction casuing the differential not to fully unlock.