1988 Fox rattle from dash

I have a 88 Fox that has had a rattle coming from the dash all winter. It has eased off a bit now that the weather has warmed up a bit. I suspect it is from the speedometer cable as at it's worst it looked like the speedometer needle would fluctuate roughly in time with the rattle. At times during the winter the rattle was very loud, you had to yell over it to be heard!

Anyone noticed/fixed a problem like this? I would imagine the parts might not be too expensive to replace but I'm thinking the labor cost in getting the dash apart might be high?

Thanks for any comments.
Simon