I just replaced the brakes on my '83 300 and repacked the front wheel bearings while I was at it. They had been set up too tight and were starting to get dry. I did the LF first, and would have replaced them but only had one set which I wanted to save for the RF if needed.

About 100 miles after the job, the car developed the noise you're describing. Replacing the bearings cured it. Pull the wheel and back the pads away from the rotor. If you can hear any bearing noise at all, change them and set the end play with a dial indicator.