x2 on the caliper. I had this issue in my Honda and it got to the point of being extremely disconcerting. You'd almost stop and *BANG*. You could both hear and feel it and it was clear it was from the front of the car. Was a caliper bolt was loose.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]