Annoying Speedometer Noise at Cluster

Greetings.

I started my '66 the other day to shake the cob webs out, and give it a bath which it sorely needed. I drove it around to get the fluid temps up to normal operating temp and I was reminded of an annoying speedometer noise this car has of which I am not sure how to fix.

Last summer, I pulled the cluster to bypass my amp gauge and install a SS voltage regulator w/capacitor. After putting it back in, I've had this noise ever since. Im not inclined to think that its the speedometer cable because it started doing it all at once. However, it sounds EXACTLY like a dry speedo cable would. I wd-40'd the cable housing and not much to my surprise it didnt make a difference. The cable is pretty free. I think the problem is in the "clock"? not sure what its called.

This car has been in my life since childhood, and as far back as I can remember, the speedo has always jumped 5-10mph while going down the road. Now, its jumping so bad at low speeds its not even legible. It levels out at like 40mph, which is way lower than my actual speed. Any ideas on what I need to be looking for? I've never had the cluster apart so I have no clue what to expect. Also, the odometer does not work, which is another clue (to me) that I have a clock issue. I have no idea how long the odometer hasnt worked. Taking the cluster out didnt change that.