Power loss / 'puff' noise when blipping throttle

[cay]

Hey folks,

Something interesting has started happening when I gear down.  I've only noticed it when my engine is warm.

When gearing down I blip the throttle to bring the engine speed up to match axle speed.  The last couple times I've ridden, once or twice I've blipped the throttle after gearing down and with the clutch still in to hear a breathy 'puff' noise, similar to how the bike can sound immediately after starting it cold.

Does anyone else experience it?  Any thoughts on what's happening?

Thanks,

C