equipment question

bought a valueline 4" centrifugal fan and am using a speed controller on it. fan isnt more than ~2weeks old and because the fan is behind the wall i could never hear this new sound. at low rps it sounds like the motor is loose or something. but at higher rpms the sounder either goes away or gets drouned out by the sound of the air fllow. though im 100% sure this sound didnt exhist when i first got the fan http://tinypic.com/player.php?v=zmi6n4&s=4 guess i should ask for it to be rma'd