I recently took over a building with about 30 these VAV boxes. They were built in 1995 and are what Trane refers to as analog units and use 3k zone sensors rather than 10k. As the air valve (damper) makes frequent, minor open and close adjustments it makes a very audible growling noise. A major temp change will cause a long r-r-r-r-r as it goes to a new position. All of these boxes seem to do it.
I have had several talks with Trane tech support about it. The local Trane supplier has had me replace the acuator motor, large plastic gear and bushings with hardly any improvement. Trane commercial tech support has no other answers and says they will call me back but don't. They always seem to be uncooperative if you are not a Trane dealer.
From what I see in the building there have been numerous attempts to reduce the noise: many parts changes and large batts of insulation on the ceiling tiles under the boxes. They may have been noisy from day one and Trane doesn't want to own up. There is a new owner of the building and he has no idea what has been done in the past.
Has anyone run into this and have any solutions?