KT735 24hp Air Leak

[CGKMGK]

I have a 24 hp KT735 that seems to have developed what sounds like an intake air leak.
Engine starts and runs just fine. No loud exhaust noise, no smoke from engine anywhere,
but at low rpm it sounds like there is an intake air leak from the left side of the engine.
I can't physically see anything and there is no hose disconnected or split anywhere that
I can find.
Could it be an intake manifold gasket or crack in the plastic manifold?
Not sure where to start first so thought I would post up the condition and see if anyone has
had this issue and if so, what's the best solution.
Thanks

 

[Scrubcadet10]

the way i check for intake leaks is WD40 in a trigger sprayer, similar to this
and with the engine running, spray down the intake, if you notice a change in RPM, (lower or higher) or the engine blows white smoke, you've found your leak. Generally an intake leak will also result in engine RPM's surging, but not all of the time.