I have the same noise, my blower has 90,000 miles on it and sounds the same as it did the day it was installed. I was told by a tire kid there was no point patching my tire, my engine was going to blow up soon. He was shocked when I opened the hood. Several of them took "Test drives" that day and all came back with a smile.
I fixed the problem by turning the radio up louder.
My set up is a 2002 2500HD 4X4 extended cab short bed 6.0 with a ProCharger and Snow performance water/meth injection, Black Bear tune and big injectors and lots of other stuff I can't remember.