Over extrusion of infill for narrow walls, nozzle grinds over print  

Over extrusion of infill for narrow walls, nozzle grinds over print

I've been getting some great results with my MK3 since receiving it last week. However when printing objects that have walls which are fairly thin but thick enough to require infill, the printer seems to 'over extrude' the infill to the point that the brass nozzle hits the part & grinds over it. Sometimes this is bad enough that I stop the print;

Other times it is not as bad, but leads to messy walls on the finished print.

When printing objects with slightly thicker walls (or parts too thin to need infill) this doesn't seem to be an issue, so I'm pretty sure it's not the nozzle height;

I've come across a few recommendations via Google, including altering the infill extrusion width &/or disabling 'ensure vertical shell thickness' but I thought I would ask before I start tweaking settings that I don't really know anything about (I've only used PrusaControl so far).

Edit - now that I've started playing with Sli3r Prusa Edition & actually looking at the infill, it looks like the 'detect thin walls' option might be worth a go - going to try it after my current print finishes.