I just bought a new D1 pro with an air assist but I don't know if it is working.

I says it has rubber feet to help with vibration but it isn't vibrating at all and it is completely silent.

I know you switch it on and turn it up to high using the dial but there is no difference. 

Can anyone tell me how noisy it should be, or is it actually working?

If it isn't working, are there any obvious troubleshoots?

Thanks