That 'Whooshing' sound can be one of two things: Low fuel level in the carb or too much backpressure in the exhaust. It's tough to know for sure without hearing it.
There are different sounds a carb will make that tells you what's going on;
This is a short video clip of a Carter ThermoQuad© being revved until the secondary air valve starts to flutter. You have probably heard this sound in TV and movies when the cops are chasing the bad guys in their Dodge Polaras...
https://www.youtube.com/watch?v=JrchxrKe76I
That's a raspy sound due to the engine not being able to handle the air/fuel charge.
A low moan is usually a sign of a lack of fuel ie; small jets or low fuel level.
This sound can be replicated by disabling the fuel supply and opening the throttle as the carb runs out of fuel. It's a dry moaning sound.