[UM2 Print Random Banding Problem]

I'll give your suggestions a try, thanks guys.

[UM2 Print Random Banding Problem]

Hi all, I've been using my UM2 with generally great results once material settings are dialed in, but even though my print quality has been rather nice I've sometimes had the problem of a single layer being indented slightly causing a slight ring around the print at any random layer. Some prints it's 5mm up from the bed and others it's 2/3rds up the print nearing it's completion. It's always just a single layer or two, never multiple rings or bands.

Here are some examples of prints showing this error:

These are old prints with a white PLA that I've stopped using, I don't have any recent prints on hand with the white ABS that I now use as I've given them to clients.

It's not every print but it's often enough to finally make me decide to write a post about it.

Does anyone know what could cause this?