Hum with Vandersteen 2wqs and passive pre?

Richard Vandersteen has commented a few times on his website that hum is a possibility when using Vandersteen 2wqs with a passive pre (such as the Placette; in my case, I'd be using a TVC). Just wondering if anyone out there has had that problem when using the 2wqs with a passive pre and, if so, what did you do about it?

Thanks for your help,
A hum problem is usually ground loop related. Connect a (ground) wire between the ground post on the 2Wq and your preamp or amplifier chassis. You may need to cheat out the third prong ground on the power cord of the sub. See if that solves your problem.