Originally Posted by europa

1/8 chains are designed for straight chain lines so aren't designed to flex sideways, unlike a 10sp chain which you can tie in knots. However, a chain is made up of lots of little bits so you'll get a little sideways flex. All you're looking for is one point that's tighter than the rest of the chain though to be honest, this'll be more obvious in vertical flex ie, the sort of thing you get when rejoining a chain and the side plates are pushed tight against the roller. The cure will be the same, use your chain breaker to push the side plates slightly apart.

I'm still not convinced you've got a problem though, just something that seems like one.