I found my rattle and feel really stupid.

After removing the driver's side lower dash panel, then driving and listening to what at times sounded like rattle from behind instrument cluster, and at other times sounded like something loose in the door, I realized what it must be.

By the way, mine is a '97 S320 and it too has the clips as previously mentioned.

I installed new Bilstein shocks about 3 months ago. Apparently, I didn't tighten the upper nuts enough. The driver's side had loosened just enough to cause this annoying rattle.
I re-tightened both sides and rattle is history.

Just for kicks, I thought I would remove the air vents and speaker grills just to figure it out. On the driver's side vent there is a hole in the plastic at the bottom. There is a sensor, presumably temperature, that is sealed on with a shiny black sealant. On the passenger side, there is some remaining sealant, but no sensor. I can only conclude that some ham handed mechanic has been in there and knocked the sensor off. Then he decided to leave it off. I see no trace of the sensor or the wires.
May have to take off the passenger side lower panel and investigate.
Can anyone verify that there should be a sensor there?

Steve
'97 S320 116K
'92 300E Sportline 242K