2005 Mercedes w203 coupé - low whistling noise from the centre dash

[Krzysztof87]

Hi everyone, low pitch whistling sound can be heard inside the car while engine is running. It's not to loud but increases when turning the fan gauge up. I have checked with open bonnet and it can only be heard from inside the car so I assume it's not from the engine. I managed to locate are where it's coming from, it's centre and left (passenger side) of the dashboard. Any idea what that could be, how to fix it, how difficult it would be to DIY or how expensive with the garage?

 

[Ted]

Just a thought, are the dash vents fully open/closed?

 

[Krzysztof87]

Just a thought, are the dash vents fully open/closed?

Makes no difference, except if I close top triangular vent, noise becomes slightly muffled but still there

 

[Krzysztof87]

Just a thought, are the dash vents fully open/closed?

Also, sometimes when I turn left it disappears and appears again when going straight