[Volvo4skier]

Well, the source of the noise was very easy to find. I opened the hood and had someone else shift between D and N while I listened for the noise. In two seconds, I found the source - it was caused by rubbing of the rubber in the top engine mount when the engine moved when being engaged and disengaged from the wheels. As the engine heats us, the metal expands, the rubber may become a little softer and there is a little less friction, so the noise disappears. So may have to replace the rubber in the engine mount.

Unbelievable, that the Volvo dealer was not able to locate the noise after two visits. One wonders what they did at the dealership or even opened the hood to listen for it. Instead, they repaired something that was not broken.