Sounds like loose tappets when idling - can't hear a thing different otherwise, as the exhaust is too loud.

The bike has around 12,500 miles on and is a 98 model. Is this an early sign of the cam chain tensioners failing? If it is indeed, is this going to be expensive to have repaired?

 

CCT's if you are to do the repair yourself cost around $100 for both.

If it is a new noise I wouldn't risk CCt failure, just replace them and never worry about it again.

 

I put APE's in and can't be happier with them, I am a motorcycle tech though so had no issue doing it myself, but its nice assurance, mine is a little noisy still, especially when cold, but with 36,000 on it and the noise not getting worse I'm not concerned...valves are in spec also...yours sounds like the CCTs though...when I bought my bike i didn't even ride it barely the first week till I got those in, not worth smashing valves and pistons

 

+1. They are known to go on the VTR. You may want to look in to manual adjusters, too. They are nice.

 

is the clutch pulled in or out??
Doesnt it have a clutch bearing rattle when in neutral and clutch released?