I just replaced the speedo in my car with one that has sat for at least a year and have a little bounce and grind coming from the new "used" speedo.
Mine is getting better but your noise could be from the speedo and not the cable.
Cheapest fix is the cable though and these kinds of things are often the type of problem that unless you want to send the speedo to a shop for testing ($$) and wait for the answer on it, about all that you can do is kind of start trying things until you find an answer.
Have you tried just lubing the cable in it's sheath to see if it is just the cold weather causing the cable to become noisy due to lack of lubrication?
You've got it halfway out so it would not be that big of a deal to pull it at the speedo side and have a helper assist you in lubing and reinserting it back into the car.
Definately can't hurt!
