W211 E270 CDI - Fan noise under engine load

[Welshmerc]

Hi,

Just noticed that there is a whooshing (airy) noise when I apply the accelerator on my 2004 E270 cdi. No loss of power is experienced but I can definitely feel air coming through the vents.
It doesn't seem to matter whether the air con is off or on. Has anyone experienced anything similar?
I would appreciate any help or steer or this.

Thanks

 

[msavill]

The heater fan does that in my w211 I have had 2 and both of them done it I am going to try to wd40 it if I can to see if it stops it