93 F250 7.3diesel, 5 spd, 4x4, ext cab long box. 250,000 kms (canada)

I am noticing a noise when in 2nd & 4th gear, sounds like a bad bearing?

Is this a common issue? Should I worry about it?

What transmission would be in my truck? How would I determine this?

If it is a bearing issue, is it better to pull it and have it rebuilt? what would I budget for that (pull it out myself)? Maybe I could find one in a salvage yard cheaper; although I'd perhaps inherit someones else's problems.

Thanks in advance.