Intermittent speedo

[Shilts]

Bought a 2002 mercedes clk320 this week and he guy didn't tell me that the speedo doesn't always read right! In the mornings the needle gets stuck at 15-20 mph although the digital reading is correct also you can hear the occasional ticking as well. Every time I have driven home from work though it's been bang on???

Have seen someone has had a similar thing in here but just wondered if anyone would known if it is an electrical thing or have any advice?

Many thanks
James