Vauxhall Zafira air circulation servos being noisy

Hi, sorry, pressed wrong button last time and can't work out how to edit post.
This is the same problem as posted earlier under heading of odd noise behind centre dash. Have done some investigation and seems to be coming from what looks like a servo unit located at front of centre console. Noise stops if heater turned to coldest setting but is not affected by turning fan up or down. Anyone come across this before? Any tips about rectifying?
Many thanks for your help.
Nick