Hey guys, I've noticed an annoying problem with my pedalboard

When I turn on some of my pedals there's a distinct clicking sound, especially at low volumes, coming from the amp. Specifically, my Digitech Whammy and BOSS DD-3.

Are these pedals known to do this?

I'm using a Modtone power plant, and supplying power to quite a few pedals with it. (Powering a line 6 DL4, Digitech Whammy, and several smaller pedals) Could this be the problem?
Lots of pedals.