Octavia Elegance intermittent humming noise from blower

Hi

I have a 1.6D Octavia Elegance estate and i have noticed an intermittent humming noise happening when the blower / heater tends to be on the more powerful settings . This sometimes causes the blower to not blow at all but after turning the blower to the OFF position for a minute or two and the trying again blower works .

I have read on other forums it could possibly be the air con compressor ?? Or the pollen filter might need changing but thought it time to ask the experts on this.

Any answers / suggestions to resolve this would be much appreciated .

Thanks in advance 

Dykey