FWIW I have always found the smallest couple of cogs to be a little noisy. I have always thought it had to do with the tighter bend that the chain is making around the smaller cogs. Limit screws control where it ultimately stops. The high limit could have an effect on the smallest cog but not the next one up. Cable tension could have an affect, but if the chain is well centered and quiet on the rest of the cogs this is not the issue either. What you are describing sounds normal to me and although it is apparent in the workstand, you will not notice it on the road.