I just took about a 20 minute ride when I shut down there was a boiling noise coming from the case. I searched and found a post with the same question but did not say what it turned out being. Just put on dyna muffler, 152.5 main jet, replaced head cap, and modified cam chain tensioner. I used suzuki oil the dealership said was recommended could this be the problem. Oh and it's a 1999.

Yes raptor will be here tomorrow

sounds like gas being sucked into engine via faulty diaphragm (petcock) or float stuck permitting gas to flood into engine..
did engine seem rich when running?

Gas would not boil in the crankcase. Sure you don't have a leaking plug on the head cover. Oil there can boil.

Not unusual to hear boiling noises in the head, most likely oil.

Oil tends to pool by the valve springs and keep it relatively cool.
on the kickstand, it all drains.  So a small amount may boil.