This is when you are pedaling forward isn't it? If you are turning the cranks backwards and seeing this, then it's just the freewheel or freehub dragging some as it turns.
You should be able to make a mark on the chain stay with a crayon or piece of tape and use it to see if the ring egg shaped while you turn it or that something is bent or not concentric with that crankset.
They do make egg shaped rings on purpose. But probably not your ring.