I think I may have this issue as well. It is like a metalic tap or dragging noise that seems to be coming from the jug. I figure it is either piston slap or the flywheel bolt.

I'm all about DIY, but I'd be consulting with a mechanic or three. Not just a Suzuki shop.

With the flywheel nut tight, and the cam chain secure....there really are just a couple things left to check.

A few members have had cam lobe and rocker wear from using oils that are too low in ZDDP levels.  Our bike does not have rollers on the rockers and the newer oils don't have an adequate level of ZDDP to prevent failure.  This sound is more on the top end and sounds like really noisy valve clearance.  You would need to remove the cylinder head cover to look at this....and it would be a good time to renew the seal on the rubber plug over the right front cylinder stud - which can cause a serious oil leak issue.

There also have been several members whose piston is loose and making a lot of noise.  If you don't find anything wrong with the cam or rockers then you need to pull the cylinder and see what it going on with the piston.  With the cylinder off you can check the condition of the rod and crankshaft.  If the piston is bad you can upgrade to a Wiseco if you want to spend money for the upgrade....or used piston/cylinders can be found for a reasonable amount.

Justin,

Knurled pistons are from the olden times. I can remember for sure after I had a piston (or two) knurled for a motorcycle engine they seemed to last forever.

Kenny G