Replacing existing manrose 150mm fan, still works but very noisy and not much flow.

Using new version of exactly the same thing, manrose 150mm fan from Bunnings, no timer, sensor, pullcord or anything fancy. Very simple, wired with a red and black, live and neutral. Switched from outside the bathroom, and using existing wiring.

Wired fan up exactly the same as old fan and... no go :-(

Put old fan back and goes.

Tried new fan again, double checked connections, all good, still no go.

Figured must be a dud, returned fan for a replacement. 

Wired up 2nd new fan and... no go :-( :-(

Old fan still works if wired in the same way.

Am stumped. Any suggestions?