The whooshing sound is more like what you would hear when opening a two litre bottle of soda pop.

The liquid sloshing sound can also come from one of your doors holding water if the drainage hole is plugged…

 

"whoooshing" is when you open the gas tank Caps and a wind of fuel vapors comes out.

 

Hello David, next time blow from the front to the back with one of those two gallon low pressure hand insecticide or fertilizer pumps with a assistant doing the pumping. Put your ear at the fuel cap, You will know what works and what doesn't work real fast.

Thank you.
Larry Louton