At higher speeds there was a terribly annoying buzz due to loosened parts inside my M47's shift lever knob. I pryed the plastic cover off (the part that has the shifting diagram printed on it), and saw that the previous owner had tried to fix it by squirting some silicon on the parts inside the knob (I think he might have cut the knob's rubber back about 1/8" to uncover the offending parts). Of course the silicone didn't hold and the buzz started up again.

In a stroke of genius, I rolled up one of those ear plugs made of expandable foam and stuck it in there and quickly put the plastic cover back on the knob. The foam didn't expand so much as to force the plastic cover off, but it did expand enough to stop the buzz. Voila!