Engine whirring noise... hmm

[Funderb]

I have a stumper for you guys, or maybe not.

Those of you who haven't tuned in lately, I've recently rebuilt ol' shitty, and stuck in new rings, milled the nasty welds out of the pipes, and generally cleaned everything up. (oh yeah, and turned the pistons back to their CORRECT directions)

Now I've got a new weirdness:
After riding around for a while, and its hot here, and the bike is right up in operating temps as it should be, the engine starts to make this whirring noise. Its weird. Its the engine itself, because it makes the noise when revving in neutral.
There is no appreciable loss in power, the clutch doesn't feel slippy, but the bike kind of sounds like a dang space ship.

or a sewing machine? spinning electric motor?

Oil levels are fine, it only happens when the engine is hot. let it sit for a couple minutes, no issue.
Its weird, and its bugging the hell out of me, has anyone seen/heard this before? I did do a forum search and found little help with matching symptoms.

Any ideas?

[dry_humor]

maybe you have it running so well its "humming" 

[adidasguy]

Isn't a well tuned GS500 supposed to sound like a sewing machine? After all, Mr. Suzuki got started making sewing machines and looms.

It is fun to evaluate a sound without a recording.

[Janx101]

errr .. trying in my amateurish way to think of whirring things ... cam chain too tight? .. very tight and close tolerances cos of new everything and it will fade? ... whirring noise hmm... tiny pfft pfft pfft noise from small exhaust leak? ...

last time mine was serviced and the oil was 'so fresh' .. it did have a slight sewing machine noise... that faded after an hour or so tho... 

[Funderb]

adidas- yeah, i went out tonight for a pretty strenuous ride, but it was cooler? so i wasn't able to replicate the sound.
I'll carry old camera around this week and see if I get it going again.

janx- im going to try resetting the tensioner to see if that might be it, it had worked itself loose when i forgot to torque them down, and I may have over-torqued the cam chain cinching it back down.

dry- I wish!  haha although with the new progressive springs it is 100x more maneuverable and responsive. The old springs were BAD.

[Funderb]

Postulate 1.0 -

When I first took the bike out after its engine overhaul, the cam chain tensioner became loose, close to 1/8" loose. (my own fault) I retightened it (engine cold) without resetting the tensioner itself. If I over-tensioned the cam chain, there is the possibility that at the present time, thermal expansion causes an extreme tension on the chain, in turn causing the whirring noise, as the chain rides hard over all the bearing surfaces in the engine.

Solution - Re-set the cam chain tension.

Corollary - Make sure to inspect the cam chain for excessive wear.