Odd splodges of filament

Hi all,

I get the odd splodges of filament appear on my models, the left is .1mm layer the middle .3mm. When it happens i hear a distinct popping sound like pressure has built up and suddenly released. I've configured the feed in rate, but i haven't got any callipers yet to configure the flow rate yet.

If i had to guess it sounds like a blockage being forced through, i'm not sure if this is a quality / contaminate within the filament or if the feed speed slows down and the stuff burns / hardens?

Thanks