SB-600 Acting up

[MindyRaeL]

One of my SB-600's is acting really odd. I'm not really sure what it's doing, but I'll try and describe it, and maybe one the gear gurus here will have some idea what's going on.

Okay, so, whenever I have my SB-600 on-camera, it will randomly make a really loud buzzing/ crackling sound and, at the same time, gets really bright and the flash kinda of blinks. It doesn't flash on and off, it just gets really bright and then dim and then bright again. And it does this when I'm not taking a shot.
It hasn't happened when the flash is off-camera with radio triggers, only when on-camera. It also doesn't happen when I'm in single shot mode, only when I'm shooting continuous. There's no rhyme or reason to when it's happening either, it's very random.

Any ideas? I have insurance on it, so I can always replace it, but I'm really hoping it's just a minor issue that can be fixed. Thanks so much for your help!

[inkista]

This is me and my Canon-gear talking, but could you accidentally have been pressing the DoF preview button? That's how you end up triggering the "modelling light" mode with an on-camera flash when it comes to Canons and EX speedlights. You get this blinky crackling instane light show as the flash pulses like mad for a while, and you run the risk of overheating your flash.

[sk66]

It's the same for Nikons *if* modeling flash is enabled in the menus.

[MindyRaeL]

That's exactly what it was! Thanks so much!