This MIGHT be typical digitizing noise that can occur with a digital effects processor when the signal level is too LOW. The signal gets down in the noise because it only uses a few bits of data which means LOW resolution in the effects processing.

Make sure your guitar is producing the level required by the vocalist.

Weak battery in amped guitar is common...REMEMBER always send the signal between devices at least at half the max volume to keep a decent signal-to-noise ratio.

ALWAYS use instrument grade cables between the devices and speaker cables for speakers... NEVER use the incorrect ones for either of these functions. They should be labelled.