HP ProBook 430 G3 - Fan

Just got a HP ProBook 430 G3, which I installed Ubuntu 16.04 LTS on. Installation went smooth and everything seems to be working, however I have one conce...

When I open Firefox and open ~5 tabs, the fan comes on and it makes this "wavy sound", not sure how to describe it, it seems as if the fan rpm increases to x, then decreases to x/2, then increases to x, decreases to x/2, this happens roughly 10-15 times in a timeframe of 20-30 seconds, before it stops. If I open another few tabs, the process repeats, but the fan stops after 20-30 seconds again. The laptop doesn't slow down at all, nor does it seem to overheat, but I am a little worried that something might be wrong, should the fan even start when I just launch firefox and (rather quickly) open 5 tabs? Also the unstable rpm of the fan is a bit strange. Any thoughts?