Ok so I have a Spider IV 30W and have had for about two years (I think)...

Today when I started playing I heard a strange clicking/distortion sound when a note is dying or "ringing out" (every time)

However the sound isn't present when playing on a more clean preset.

I guess the noise is there all the time just that I can't hear it when I'm playing.

The sound is almost exactly like this http://www.youtube.com/watch?v=upPiJ9vOYiY

Except that it's a bit lower and more "guitardistorted"

I've been using the same setup on the amp for about six months so it isn't any problem with to much gain or such.

It isn't the guitar nor the pickups because I've tried two different guitars (one with active pickups and one normal)

and it's still the same noise.