Issue with Circular Objects being irregular?

I’m starting to notice something odd. A few small object prints that have round holes in them are appearing oval in shape… I just started noticing this yesterday. The main body of the object is square, and that’s turning out ok. I need to do some more tests, but does anyone have any thoughts about irregularly shaped holes?
Just for reference, I just started printing with a new spool of white ABS from Gizmo Dorks.
I tweaked the Cura settings a little and set the filament diameter to 2.85 and the wall thickness to 2mm.

Dower

Try tightening your belts.