Yesterday, my 2011 Impala LT started making an odd tapping noise. It'* coming from somewhere on the passenger side of the dash and comes in an irregular cadence. It'll tap a couple of times and stop, then tap again four or five times, then maybe two or three times, then maybe a dozen in no set pattern. The noise will also persist for 10 or 15 seconds after I shut the engine off.

It seems to be related to the HVAC system because I can make it go away by pressing the button to put the system into recirculating mode. It only happens when the ventilation is in pass-thru mode.

I replaced the cabin air filter earlier in the week. Could I have messed something up in that process? Any insights would be greatly appreciated.

Could be a bad "gear" in one of the HVAC actuators, and sometimes it is "searching" back and fourth....

After doing some careful listening, I've determined the noise is coming from the vicinity of the vent closer to the passenger front door. Oddly enough, the tapping will now also start up when I unlock the doors or open the trunk with the remote key fob.

I just ordered a blend door actuator or just under $14 on eBay. Hopefully that will solve the problem. It'* getting annoying to listen to.

The part came today and I installed it in about two hours. The actuator that was acting up was indeed the one on the far right. The good news is only two screws were holding it in place. The bad news is they were at a very awkward angle with precious little room to work. I ended up losing the old actuator behind the dash but I had to make a choice to save it or the second screw. It'* not in the way and now there'* no more tap, tap, tap. One thing the YouTube videos I watched didn't show that really helped was to remove the interior of the glove box from the lid to gain more space to work. Take the latch mechanism off first (three torx screws) and then remove the box (four Phillips screws).