1997 Chevy Tahoe Wipe Motor

Everything works just fine, even the A/C. But for some reason when I drive the car the wiper will work and sometimes it will not.( If I restart the truck no luck ). Even when it doesn't want to work and I turn the wiper switch to full it will make a buzzing noise from the colum like the motor wants to work, but the wiper itself wont dont do anything. Is it the motor. Or a electrical problem. I hate driving in the rain with no wipers.