So, my '02 GS500 has the sound that competent mechanics tell me is my cam chain. However, I replaced the tensioner and the bike still makes the sound. Yet, a pro motorcycle mechanic told me he only hears it at idle speed. The sound goes away if given some throttle. My question is, is this a familiar issue with the gs500? How bad does it need to be replaced if it is totally stretched out. Also, how hard is it to replace? I hear its not an easy job.

I'd confirm what the noise is first.

Get a mechanic's stethoscope and isolate where it is coming from.

Two different mechanics told me it was the cam chain although I think one of them said it could be a worn guide. Are you saying it needs to be narrowed down even more than that?

Just a suggestion to isolate the noise as best as possible.  Been there...you hear something, immediately suspect something...only to find out it's something completely different.  I'm sure you did this, but did you check to make sure that the tensioner is providing the correct amount of tension on the chain?

Valves adjusted recently?  Is the clearance too loose?  If so, it causes a tick tick tick noise that may mimic the valve chain.

All I got.

I'll check the tensioner again but after looking around on the nets, I'm thinking it could be the fabled "cam end float" since its only on idle.

'02's have the spring washer that eliminated the cam end floating noise. Somewhere around 1997 the change was made.
A recording would help.
Worn cam chain guides are easy to replace. Hard for them to wear out. Maybe the top rear one is loose or missing? It is a small triangle shaped one.
It could be something else. On Junior, we thought he had cam float noise until it got worse and the counter balancer bearing went out. Had symptoms of hearing it at idle and revving would make it go away.....that is until it finally went out then it was REALLY LOUD and the engine got very hot.

gsJack said he had it on his '02.  http://gstwins.com/gsboard/index.php?topic=57931.0

Anyway, I will try to get a recording of it on my phone and post it. Hopefully the sound quality will be good enough to hear it well.

The 02 didn't have the spring washer cam side play fix.  Change was made around 05.  My 02 had a bit of cam knock for a while same as my 97 did.  Both stopped doing it after a while.  The knock was a bit annoying but harmless.

There's no confusing a really noisy cam chain with the sideplay cam knock if you've heard both.  I had a Honda cam chain a bit loose years ago after it was missadjusted a couple times and I can still hear that noise now.   

Both my 97 GS I put 80k miles on and my current 02 GS with 97k miles on it have had a trace of cam chain noise off and on but I've considered it harmless. The GS cam chain tensioner takes up the freeplay a notch at a time and it seems the chain can start sounding noisy a bit at hot idle just before it takes up and quiets again.  Dunno, I won't worry about it until I hear the big bang.   

First sighting of it is in the 2004-2006 parts catalog.
Though in all my older engines, I never heard anything annoying with the cams. They always are pretty quiet as is others that show up with older bikes.

If someone removed the cams and forgot the washer on the left end of the cam shaft, it would allow for lots of bounce. With the washer in there, they are pretty tight with little room for making noise (at least in the engines that have been to the Bike Cave).

Found the Suzuki Service Bulletin covering dealer warranty fixes on 04-05 models so the change at factory must have been after that.

http://www.sportbikes.net/forums/attachments/suzuki-line/107537d1166036602-gs-gsx-gsx-r-139-revised-gs500fk4-k5-engine-knock-idle-asmc_004983.pdf

Interesting that the exhaust buckets also get changed. Most likely noise came from the exhaust side. In older bikes (89-2002), there was the tach cable and gear which probably put a little load on the exhaust cam so it wouldn't tap back & forth.

Weight the chain and measure the distance across the centers of 20 pins in a straight line with some verniers, service limit is 157.8mm.....its all in the manual   

Not sure if you can do it accurately with the head or even the block on though 

Need to split the cases and lift the crank out of its bearings to replace the chain so its major surgery. If you are going to do the job properly there are also 3 sacrificial guides to replace, 1 long one at the front of the tunnel, one short one in the top of the valve cover and the little triangular shaped one at the back. Also the tensioner blade and.....if they show signs of wear both camshaft sprockets otherwise you new one will soon go the way of the old one.

Its a big job......personally I would live with it and until the noise becomes unbearable or it lets go big time and then drop an ebay motor in

Sounds like cam end float noise if it can only be heard at idle. Mine does it when it is warmed up. A quick rev gets rid of it. By the way mine is an 04 GS. Must have been 05 as GSJack said when they fixed it. Apparently it is not terminal.