Mine did something very similar (hiss/chip type noise) only in the driver side front, and only after I hit a large pothole. I could only hear it with my window down. Still not sure if it was the shock or the mount or what, but the shock was replaced and the his/chip disappeared.
Sounded a bit like a short burst of letting air out of a bike tire valvestem (hiss?)
Hit any big stuff lately? Is it on only one shock?