Few years ago working at a glass shop, there was some stuff we called felt, put you in the mind of the tar paper used on house roofs before the shingles were put on. The felt was pushed down into the window frame & then the glass installed to make the glass fit tight in the frame.
Once in place, the extra felt was trimmed close to the frame to finish the job.
The felt came in different thicknesses & was just a mater of picking the proper thickness to fill the frame channel.
Check at a glass shop for some of that, get several pieces & different thicknesses & then pry the rubber seal up out of the window frame & install some of the felt in the channel, push the rubber back in & walla, window tightened up to keep from rattling.
I know what robatthelake is saying, cause I drove a Dutch Star like in his avitar a few trips & the drivers window shook all the time or either wind noise from being cracked open. If it had been mine, I would have taken the time to fix the problem, just didnt have permission.
Neil