4WD Hi ticking in a 2000

[jasonmi]

Hi,
I'm looking at possibly purchasing at 2000 Tundra Limited with about 113K miles on it. I test drove it this weekend and it rode great in 2wd, but when I engaged the 4WD HI, I noticed a ticking noise as I was driving. It wasn't loud, but it was noticeable. It was fairly fast and about every 6-7th tick was just a little bit louder than the rest. I liked the truck other than that, but this noise has me a little concerned. Any ideas what it might be and what I might be looking at for repair costs? The guy wants $8900 for it.

Thanks,
Jason