Rattle when climate control is on -C280
 

While running the A/C after a half hour or so in my C280 in all types of traffic conditions, a rattle begins to eminate from somewhere when braking to a stop. It increases in intensity as the car slows more, and dissipates to a light rattle when at idle. If I switch the climate control unit off the rattle does not make itself apparent.

Any ideas as to the source of this problem? The car now has 197K miles and this has been happeening since roughly 87K miles.

possibly a belt tensioner shock???