I recently took apart the top end of my bike and put it back together with fresh gaskets and a new exhaust valve.  Since then, I am hearing what sounds like cam chain noise.  I can't hear it at idle, but from 4k-6k RPM it is very noticeable.  The noise is RPM dependent, not speed dependent.  I had a mechanic who has previously owned a GS500 ride the bike, and he also thought the culprit was the cam chain, and that it was louder than it should be.

When I last worked on the bike bike, the stock, automatic tensioner seemed to work fine.  I was very careful, and reinstalled everything per the manual.  Could it be that the tensioning spring is just weak at its advanced age of 15 years?  Really, there is no cam chain noise at all under 3k RPM. Over 6k RPM the bike's exhaust and the wind drown out the noise.

Should I bite the bullet and drop $50 on a manual tensioner?  Will I hurt anything by riding the bike in its present state?

Be sure the front and back guides are installed correctly. It is easy to NOT get them seated where they belong.
Insure the rear tiny wedge guide is there as well as the one across the inner top center of the valve cover.

The top end is open right now, and all guides are installed correctly, including that little triangle one.  I remember seating them very carefully multiple times when putting the top end back together.  There is about 1/8-1/4 inch of play in the cam chain.  The chain feels very tight, but there is that little bit of play.  Is the play much?

Also drained the oil to look for metal shavings and couldn't find any.  I am puzzled!

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Last weekend I removed and tested the cam chain tensioner and verified the guide was propertly installed.  Everything was then put back together and torqued to spec.  I am still getting noise when I rev the engine, and I don't know what the problem is.  The noise began after swapping in another top end and replacing all the gaskets.  A new stock exhaust was also installed at that time.  Here is a youtube clip of the noise.

http://www.youtube.com/watch?v=h4CJ2K9ejGQ&feature=youtu.be

The noise in question is most noticeable at the 5-15 second range, when the engine is reved.  There are no other symptoms other than that noise.  Help me find the problem!

Sounds the same as my engine, actually. I'm just about to put a new head gasket on to see if that does the trick.

But as far as yours goes... try grounding one of the plug leads and trying again. Then do it with the other. That'll tell you if it's combustion related at least.

Had this same exact sound in mine. Tore the whole engine apart and could only find a lightly damaged rod bearing. Search for my thread: terrible engine noise

Ended up putting a new engine in. Ever since, haven't been able to get it to start due to electrical issues.

I have narrowed the sound source down to the lower end, and I think the left side.  I was actually in there yesterday after making the video and the generator looked normal. 

Any luck tracking down the cause of the sound?

No luck.  I am convinced this is cam chain related as the noise is even there with the clutch pulled in.  Has anyone ever had the tiny part 9 from this part diagram get knocked out of position?  http://www.bikebandit.com/1998-suzuki-gs500e/o/m22269#sch237723

I wonder if that could be the culprit.