replace tensioner with serpentine?

At 115K, it couldn't hurt. It would also give you some peace of mind. You'll find that more pulleys are available because the bearings fail more often. The tensioner itself can bind internally and/or break off completely, but it's not as common as a failed bearing. It's like an alternator or water punp. It might last 5 more years, or it could fail next week. I've seen just enough of them fail that I, personally, would replace it. It's a judgement call.

The tensioner should be good for several belts.

Next time you start it up cold, lift the hood, listen for pully bearing noise.

There's a pully on the tensioner, another on the idler arm. Pullys are maybe $16 ea.

If the car's real solid and you plan to drive it for many more miles, maybe remove tensioner and check for wear. It's the pullys that usually fail.

"Mit der Dummheit kaempfen Goetter selbst vergebens!" -Friedrich Schiller

I've had some noise for many miles now, I figure its one of the pullys. Will I be able to tell if one is making noise when I have it all off?

Will it sing a song for you when you hold it in your hand? Maybe not. :-)

Release belt tension (with 1/2" breaker bar in tensioner receptacle on my 94 Tbird). Reach down and wiggle pully. You should be able to tell if bearings are bad.

"Mit der Dummheit kaempfen Goetter selbst vergebens!" -Friedrich Schiller

I use the old trick of using a long tube (recently a 2 foot piece of pvc pipe) or a long screw driver or....... While it is running place one end on or near the bearing area, the other up to your ear. Never failed me.

Once its off, you should be able to tell by the feel when you turn it. Once its off, cheap insurance to replace it, especially if you have a vice and can just replace the bearing by pressing the old one out, new one in.