hissing when letting off throttle

[1stimer]

It's been a while since I posted, but I cant find anything on my problem. First of all my '84 123 is doing great. I had some vaccum problems that were driving me nuts, so when I shipped the car back here to the Mainland I had Enrique work his magic on it. Took him all of about 10 minutes to track the leak down. I still have a plugged climate control vaccum, but that's ok for now.

Anyway, ever since then I get a hissing sound when I let off of the throttle after acclerating. Anyone ever have that problem, or can point me in the right direction? I have also noticed more smoke under full throttle after a stop.

Anyway, it doesn't seem to be too life threatening, but it sure is annoying. Just ordered some new brake pads from Phil and will attempt my first brake job on the Benz next week. I've had the car close to a year now, and haven't done anything but oil changes. It's been great. (fingers crossed).