Click on outputs?

[Vexx]

I have 2 Virus C's & this problem is the same on both.

Some sounds seem to generate a loud click after some notes are played. It doesn't happen as you would imagine as the note finishes or even at the start from a fast envelope setting. The click seems to be delayed, almost like you'd imagine a kind of shut off from the synth engine.

It's driving me mad as I can't seem to find a logical answer.

Anyone shed any light on this?

Thanks in advance