Hey, This is a really weird issue - Part of the problem is the noise is so hard to describe but I will try my best. The sound: It's a really high pitched "Teiow teiow" with the emphasis on the "ei". Think a really fine wire snapping when under tension, similar to a guitar string, but this happens multiple times - maybe 6-7 times. Or another way would be the noise that a pot of really hot oil makes. That crackley noise kinda. Or really quiet fireworks, the zeeeeooowww noise, not the bang.... It's a weird noise. When it occurs: The first time I noticed it was on the 40*c days last week. Sitting in 5th, lugging a long and then twisting the throttle hard. But it only made the noise 2-3 times instead of 6-7. The next time I noticed it was again on the 40*c day. After zipping through traffic moving at irregular speeds do to a diversion, I used the clutch a lot and sat in first/second to announce my presents to the disgruntled car drivers. This would have got the engine quite hot. Then after I got out of the traffic and started using the clutch again, particularly between first, second and third gear it would make the weird noise. Worse from a stop. Today (Only 20*c outside), the bike didn't make the noise at all all the way to the city, similar to the other days - it doesn't seem to make it when cold. But after I got to the city, after clutch work through traffic and an hour of riding I stopped at a set of traffic lights that are on an incline. When taking off from the set of lights, on the incline and after the traffic work it made the noise right before complete release of the clutch. The last sixth of the clutch. Mechanics Opinion: First off - the mechanics couldn't not reproduce, as it seems to be when the bike is very hot and under additional load. Judging by my description of the noise and circumstance alone they told me it was engine "pinging". I googled what a pinging engine sounds like and it didn't seem to sound like that. Some evidence to support their conclusion is that I do have basic aftermarket slipons with no tune or air cleaner upgrade. That being said, I was told the particular set of slipons I have would not require a retune. Possible additional note: I've noticed that the gasket that connects my rear slipon to the balance pipe is deteriorated and leaking exhaust. Could this be related if it was a tune issue? What is going on guys? Ideas?