I have a turntable (Project Debut III) that is producing a low hum (not
rumble - no pumping woofers) during silent sections of the record. It
is grounded, and the transport screws are removed. There is very only a
very slight (volume past halfway to hear it) hum when the needle is not
on the record, and this can be stopped by unplugging the CD player.

Can I assume that it is not an interference problem? Does anyone have
any ideas why this might happen? The motor seems to be vibrating a
little when I touch it, but not audibly, and it is suspended from the
plinth by an "elastic band" type device.