I don't think you are hearing.... belts die for two reasons.... wear as in miles.... and age as in time. old low mileage belts look good... they measure well... to the surface they look fine
but they are old
old tires have great tread.... on the surface they look good but they fail because they are hard and brittle
do not go by one thing.... consider both.... age AND miles...
otherwise... I have a couple of 15+ year old 19" tires off of barn finds I will cut you a good deal on... lots of tread left, one even has the nibbens… they measure good! And for being old they are stiff!