[blkz650]

 

[Tremonte]

Add fuel. Vapor build up in the tank. What you hear is the venting through the seal, probably caused by warm ambient temperature.

 

[Nate]

That happens with my bike sometimes on warm afternoons once I finish a ride. Just open up the fuel cap, you'll hear the pressure be released, and reseal for no more noise.

 

[Shamsul Kamal]

I suspect the that noise is due to tank vapour. Thank you for the confirmation.