A possible issue is that the rubber tire on the bearings (there are two bearings under the rubber tire) is rippling as the scope rolls on it. If the adhesive has failed or has not been properly applied, as the scope bearing rolls on the tire, it will ripple up in front of the bearing causing unsmooth movement.
There is a simple solution and in time it may just provide itself for you. If the tire feels loose to you, just peel it off. If it is loose, it will walk off the ball bearings all on its own one day.
This happened to my scope in the first six months of ownership. When the first one walked off of the bearing on its own, I just removed the other one and never worried about it. I don't know what purpose the tire serves and it just creates unnecessary rolling friction. My scope worked fine without them for over seven years.
Just something to check. If it is stuck on tight it is probably fine, but if you can squirm it around, I would just remove them all.
Edited by Eddgie, 24 September 2020 - 03:23 PM.