Tick-tock noise from vents: depends on temp selection
 

I'm getting an annoying "tick tock" sound at about 1 second intervals coming from behind the radio, but it stops when you set the temperature to a slightly higher setting (about 9:00 on the climate control dial). When set to almost full cooling you'll get the noise, even when the fan switch and A/C are both off. It's got something to do with the temp selector. If anyone else had that happen and got it resolved I'd love to hear how it was taken care of and what it is. Thanks.

What year?? the 1998-01 ML's have a "blend" air door that is moved by a motor..they fail & make that type of noise.

99 Ml430
 

It's a 99 ML430 with about 89K miles. The cooling actually still works, BUT, from time to time you'll feel a pulse of slightly warmer air come out, then it cools again. This would be consistent with a malfunctioning flap controller like MBDOC describes.

Q: is it easy and/or cheap to fix ??? Sounds like you'd only have to remove the radio and the panel to get to it, it sounds REALLY close to the front of the panel as opposed to being way back in the dash somehwhere.

Dash removal is required...approx 5.5-6.5 hrs labor