a/c - dash center vent wheel noise?

[bosanci28]

i notice on my 2003 x5 4.6 , when i turn the a/c the dash center vent ,behind it i hear like a wheel noise,it does off and on,when it does that noise ,if i turn the a/c off it stops!,

is it something i need to change ?

anyone had this problem? before ? how you fixed it ?

thank you,
misu