I use 90% glass call while hunting. If your call is squeeking on you then it's not surfaced right. I want a squeek in my glass calls, but a very short squeek right at the begining of a yelp, not half way through it. If it is squeeking a lot then your surfacing it with too fine a grit, all I use is a stone, courser the better, if I'm using sandpaper then it's 60-80 grit especially with bronze glass because of it's hardness. Once you have a glass call conditioned right it will play easier than any slate ever will.
WI Youth & LTH Mentor
Dodge Co. NWTF