It is the belt that chirps in the rain. It isn't discussed too often because most riders try to avoid the rain. Also, most riders have a belt guard which keeps the light spray off anyway.
There has been a lot of controversy about how to adjust the belt, and for the most part I've been the "old fart" that figured that the tension gage and MOM were the only references to use to adjust the tension..."by the book". But this year, I tried it differently because when I needed to adjust the tension, I couldn't find the gage (I found it finally).
Put the gage back in the toolkit, and use the "90 degree twist" method...grabbing the belt mid way on the lower side of the swingarm and twisting. When it is loose enough for that, position both wheel adjusters to the same marks and tighten the axle.
I think this method actually sets the tension looser than the gage, but it works great. The wheel rotates easier, there isn't any dry squeaking, and during my 22 mile interstate ride home yesterday...in the rain...not a sound.
BTW - Kropachek and others are the ones that introduced me to this adjustment method....they get the credit.