'97 E420 - couple of months ago AC compressor starting making a clunking noise for a second or so after clutch engagement. Now, with the HVAC fan at low speeds, the clunking noise can also be heard during moderate braking; with the vehicle at a standstill the noise stops. Otherwise, the system cools well.

Is compressor failure imminent? Should it be replaced now, to avoid the potential for contaminating the refrigerant lines with metallic debris?