Hum Problem with Grado

I recently helped my friend set up his VPI Aries Extended. He is temporarily using an inexpensive Grado ($80 Red?) cartridge but we are hearing significant hum. We grounded the table, which helped, but the hum is still very noticable. Anyone have experience with hum using a Grado and how can we solve this problem? Rest of the system is AR SP16 and VS110 w/ Proac Response 3s. Thanks.