Odd Noise from PickUp

I just bought the Getaria Wireless System, 2.4 Hz model. It works fine with several of my Ukuleles. But on one with an LR Baggs Five 0 pickup, it produces a clearly audible constant tone that sounds about the same pitch as my E string. The same Uke sounds fine when played with a wired connection to the Amp. Does anyone have an idea about why that's happening?