Here's a Mach 8 parts diagram
I'd be good to remove Parts 1 and 2 (possibly 3) and clean everything out. PLEASE DON'T order any parts from this, since it appears to be Aussie and set up for 240VAC!
Your Mach 8 uses two motors. I'm not familiar with those, but I can say for certain that our Mach 15, with a single motor driving indoor blower and outdoor fan, has never frozen up on HIGH fan speed. It has on LOW.
I think the "whoosh" noise is being caused by frost, and cleaning, a clean filter, and HIGH speed, will keep it from frosting in use.