AC 'knocking' sound from vent below dash

I have a 2007 Ford Escape Hybrid. When running the AC, I hear this knocking sound coming from under the dash on the passenger side. It sounds like some kind of valve opening
and closing quickly, over and over. It isn't continuous, but it will occur at least every 10 seconds. It might knock 2 or 3 times, then not at all for several seconds, then once again, and nothing for several seconds, etc. I think I found the device making the sound. I can feel the vibrations of the knock coming from this device under the dash on the passenger side:
http://img253.imageshack.us/img253/4322/escapeacmodule.jpg
Anyone know what could be causing this sound? It only knocks when the AC is running. The cooling power of the AC doesn't seem to be affected by this problem. Before I shut off my vehicle, I always turn off the AC and let the vent run. The knocking will slowly stop over the course of about a minute while the vent runs. Then when the vent is blowing warmer air, I don't hear the knocking sound at all.
Any help would be great.
Thanks!
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In article <e41f0d7e-f590-4e49-9ae7-

It almost looks like some control motor? Maybe the damper it controls is knocking on something, or loose and flapping.
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it is an 07. it should still be under warranty, rite?? why not just take it back to a dealer

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I cannot tell from your pic which one it is... but this is a controller for one of the "doors" in the heater plenum (most likely temperature blend door). As has been noted, this is covered under the bumper to bumper portion of the warranty.... I'm in Canada so all I can do is guess at US coverage being 3yrs/36,000 miles.
There have been TSBs covering these controllers though I don't recall any specifically for Escape or Escape Hybrid... Your dealer should be able to run OASIS to see if there is a streamlined diagnostic... As it stands, there will be some simple testing to verify that it is, indeed the controller causing the concern.
FWIW, there may be a difference between EATC and MATC so one should endeavour to include all pertinent info in a help request.

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Unfortunately, the warranty is 3 year / 36k. I've already exceeded the 36k. So, I'm on my own. If it is indeed this device, is it something I can easily replace myself? All the coolant won't come out if I remove this device? It's pretty easy to access, and it appears to be held in place with 2 screws.
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There is a slightly better than even chance that this is the faulty part... depending on the price, this may count as "inexpensive diagnosis". With the key off, disconnect the electrical connector first... remove the old device and install the new (sweep the door by hand to be sure it doesn't bind and there are no obstructions) controller before connecting the harness...
Trying to operate the controller without having it properly installed can mess up your day....

Unfortunately, the warranty is 3 year / 36k. I've already exceeded the 36k. So, I'm on my own. If it is indeed this device, is it something I can easily replace myself? All the coolant won't come out if I remove this device? It's pretty easy to access, and it appears to be held in place with 2 screws.
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Is this something I can get at a parts store, like Napa, Checker, AutoZone, et al ? Online? Also, what is this thing specifically called?
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