Every print with 0.08 layer end up with this “micro-ringing”. PETG (couple brands). All the calibrations done. Flow ratio, flow rate, temperature seems to be irrelevant. If speed is low the result is a little better, but still there. Possible extrusion gear issue? The gear is clean as brand new - I checked it, but I notice that the gear in the bearing is totally loose. I did not need any tools to get off the gear from bearing.
Have you tried increasing the layer height? .08 seems to small for PETG to me.