At low speeds (idle) the backlash in the gears make the Comptech sound like a cement mixer full of gravel. Off idle it sould go away and be replaced by a pure whistle. No telling what freaked out your mechanic.

A sound clip might help.

 

Here's a video that will let you see what my Novi 1000 sounds like. Keep in mind that this is with the camera/mic only a couple inches away from the snail. It's not nearly this loud unless you put your ear very close.

Novi 1000 Concrete Mixer - Please right-click and save-as.

 

thats exaclty how mine sounds- thanks man, that was perfect.

 

Sounds great

 

Sounds great