I was also having some 'noise' behind that part of the Dash. It's a quick and easy job to carefully pull out the front fascia, and then carefully unclip various things to get to that small motor-driven fan. Over time, dust gets onto the moving parts of the fan, which causes friction, hence the humming or buzzing noise. Use compressed air, a very soft small brush, and use a TINY TINY TINY amount of lubricant for the motor spindle. If you use too much lubricant, any dirty air and dust that is sucked through the vent will still, thus causing the same issue. The plastic fan simply slides off the spindle. It solved my noise issue immediately - Absolutely silent. That was a few month ago I think.