Bypass Clicking/Popping

[Mr.Durden]

Ok, my pedal board is the followoing:

Guit -Whammy IV-Boss OC2-Line 6 FM4-Boss SD1-Ibanez DE7-EHX MMD-AMP

So, ive had the whammy for a while, and noticed that it makes a clicky poppy sound when i bypass or unbypass it, especially noticeable when the overdrive is activated, but i learned to live with it. I recently aquired the line 6 FM4 Filter modeler, which supposedly has True bypass switching and noticed that it does the same thing, it makes a clicking/popping sound that is heard through the amp when the efect is activated or bypassed (not when switching through efects though). Is this normal of digital effect pedals? if so why? My other pedals dont seem to do this.

Thanks in advance