Ok, another post from the XC90 newbie - different topic this time. The car seems to have a HVAC blend door that is making noise - comes from the dash, very plastic growling sound - does not make it all the time, just occasionally. I am guessing it is either a blend door or temperature door gearbox?

Of course I can do some further experiments to determine which it is, like:

1. Set the blend door in a single position and see if changing the temp setting makes the noise.
2. Set the temp door to full hot or full cold and see if changing the blend door makes the noise.

The question I have is more related to the cause and the corrective action. My sons Tahoe had a blend door issue, but it was more of a catastrophic failure - gear just snapped in half. My questions more specifically are:

1. Is this common on this model?
2. What is the root cause and most applicable corrective action.
3. Best place to buy the needed part?
4. Where is the culprit located, and how do I get at it?

OK, full disclosure, I have not done a search yet, so I will do that now and remove this post if necessary.

Thanks in advance for any help.

Tim