Hmmm...I'm not buying that the caliper's making noise. I'd guess that your parking brake is adjusted too loosely, and that's what is knocking around back there. Had this happen on my 500E. Adjusted the P brake; noise gone!
"If everything seems under control, you're simply not going fast enough" --Mario Andretti
1995 E500 street car
1986 Porsche 944 Turbo S track car