Screaming speedo

This is strictly a cold weather problem (real cold, usually has to be 15 or below), some days, like today, when I get on the freeway, actually as I hit the ram and start to accelerate, my speedometer will start a almost painful, high pitched screaming (the neddle also shakes a little). It will usually stop if I drop my speed below 30 or so. It always stops after a few minutes. Happened just a couple of times last winter, and its happened maybe four tiems this year (so far). I doubt that its damageing any part of the truck beyond the speedo cable, but who knows,

Anyone else have this problem? How, if at all, have you dealt with it?
A mechanic said that basically the cable was dry, that they are sealed, and that I'd just need a new one (which is apparently a big, dropping the tranmission kind of deal).

It hurts my ears, as well as my soul, to hear my truck cry like that, help.

Oh yeah, 1997, 167K.