Heater/Aircon is making a whistling sound when turned on, the fan has 4 speeds, on speed 1 you can't hear the whistling noise but the higher you turn up the speed the louder the whistling noise. The noise is on both hot and cold settings and only subsides when the fan speed is turned down too 1. I recently changed the pollen filter on the car as the old one was filthy. 

Any idea what could be the problem

Thank you 

Might sound daft but have made sure all your vents are fully open because if one is slightly closed it will cause it to whistle

What tune is it whistling? Also, you have been nominated for the longest thread title in the history of long thread titles.. 

😁

yeah mate i have tried that and the whistling is still there.

Just now, mozz said:

What tune is it whistling? Also, you have been nominated for the longest thread title in the history of long thread titles.. 

😁

Haha, I typed it in the wrong box 

Are you sure the pollen filter is seated correctly?

Have just checked and the plastic cover is missing three screws so it's not fitting snug so the air is getting out from the pollen filter housing, I applied pressure on the cover and it stopped the whistling sound so just needs three more screws and that should fix the problem

Thanks for the help