The speedometer in my PV has been doing the same thing - it made a racket when the weather got colder, which would, eventually, go away after driving about 5 miles. Because the trip counter had ceased functioning as well, I just finished taking the thing apart and replaced some of its innards with bits scavenged from other speedometers. BTW, that works only to a certain extent because there are some subtle differences between early and later speedo units which limit the possibility of exchanging parts. I don't know if the transplants were a success because I haven't got around to putting the unit back in. Next confession: I don't really know where the racket came from. I'm assuming lack of lubrication -- either on the gears that drive the odometer, or perhaps on the shaft that spins the magnet that makes the cylinder (ribbon) turn -- could be wear in, or around, that shaft as well. The cable is new, and I loaded it with a mixture of anti-seize compound and engine oil, so I doubt that a dry cable was the cause. The rotation of a magnetic disk moves the cylinder against the resistance of a spring at the other end. There is a metal worm gear, spun by a gear driven by the end of the cable as it spins the magnet, that mashes with brass gears on a couple of shafts that move the plastic gears that move the number wheels in the odometer and trip counter. Each of the number wheels has a tiny spring-loaded ratchet in it to make the numbers advance only when the car is moving forward. In my trip counter the ratchet on the firtst, white, wheel was worn and slipped. I find it hard to believe that that was the source of the rattle because it's such an itsy-bitsy little thing. But, who knows. Anyway, I put a tiny amount of bearing grease on all the metal gears and am hoping for the best.
So, now you know all I know about these speedometers, which ain't much, but might help.
Good luck,
Bob S.