Strange vibration but nothing seems crooked

Short history:
Bought an 85 vf500. After cleaning carbs, went for short run. Seemed fine.
Had good tires on ugly spray bombed rims swapped to nice, straight stock rims.
Got the rear wheel on. I did swap rear sprockets. Same teeth. Same condition and both flat with no cupped teeth. The newer one does have a chain guard. Now, when I idle on the center stand, there seems to be a vibration, side to side, at the back end and a slight sound, like a sticking tooth, at the front sprocket but I checked and rechecked the chain and sprockets and wear pad and nothing seems wrong.
I may just swap the sprockets just in case but apart from making sure that both sides are equally spaced and tightened, using the rear wheel take up bolts, is there another procedure to make sure front and rear sprockets are aligned?

 

I used to check alignment with a long straight edge on the rear wheel.
Check space to side of front wheel on both sides.
If one side has smaller gap, the front of rear wheel needs to move in that direction.

 

could be a worn-out chain, so check for a series of loose-then-tight spots along the chain as you rotate the rear wheel. and when you adjust chain tension, be sure to find the tightest spot and set proper slack there !!