2001 Dakota Valve tapping noise

I'm considering buying a beautiful 2001 Dodge Dakota 4WD 4.7 V8 engine with only 116,000 miles that has obviously been very well taken care of.
The owner let me have it for the day and I had it thoroughly checked out.
The only thing that kind of bugs me a little bit is the fact the the engine has a very slightly audible valve or tappet tap. Its as if one of the valves may be making a little bit of noise at idle, but when I run the RPM's up and the oil gauge indicates higher oil pressure this slight tapping sound seems to go away.
The price is really right on this truck and I'm wondering if I should walk away from it just because of this very slight tapping sound.
Any ideas what I might be hearing and is it a real critical issue?
Thanks!
Harkauto

I ran into a guy in the garage today that told me he has experienced the same thing with his 4.7 engine in his Dakota and his tapping noise went away when he switched to Mobile 1 synthetic oil.
Has anyone else experienced the same thing?

Anyone Dakota owners out there have any experience with this or got any comments for this issue?