Hum on SC p/u

Hello
I play a G&L SB-2 out of a GK mb112 combo. The single coil pickup on the bass, when soloed, lets off an hum from the amp much like single coil pickups on a guitar (I am new to bass). What can I do to get rid of the hum on this pickup? The amp is still in the return window if an exchange is recommended.