They're actually ventalation fans, mostly used for marine purposes. If you're into boats, you will probably know that before you start inboard engine, you turn on the blower, to get gas vapors out of the engine compartment (so you don't blow yourself to bloody hell) well, that's what those fans are - they're freaking $12.00 marine blower fans.
I saw a thing in the back of a magazine that had a horn that would "Make real turbo sounds!" programmable to the rpm level you wanted then it would make the noise of a blow off valve. I can see a bunch of people doing this too, that's what's sad.