is it when using the echo? if you had a long echo on previously, sometimes it is still playing when you turn the effect on again; this might be what you're hearing.

Dizz, can you go on to the 57 setup panel and check which firmware you are using.

v1.11
This is with a kaoss pad, nothing to do with tails of delays but cheers for trying.

The Kaoss pad may have some DC offset on its outputs, which would definitely cause switching noises.

If you want to be sure it's not a problem with your mixer, try connecting the effect sends and returns together with a single pair of cables, then see if engaging the flex-fx switches cause any pops in the audio.

So is this an accepted fact?
I did the in straight back to out thing and there was no pops but that doesnt really help me!
i havent had this happen with any other mixer...
D

I don't get any pops with my EFX-500

Anyone else use a kaoss pad 2?