Strange sound when braking

Cubic Posts: 594
edited January 2012 in MTB beginners

I got my first mtb a couple of weeks ago. When using it recently I noticed a few times that, when I apply the front brake, there is a sort of bubbling sound. It only happens when I first pull the lever for a few seconds, but is a distinct liquidy bubbly sound.

I took the bike to my lbs. They couldn't replicate it, but said it's unlikely there's an air bubble in the brakes (Elixir 3) as that wouldn't produce a sound that was audible when riding.
They thought it could be from the disc itself, hitting the pads, or from part of the front suspension. But they weren't sure.

I was wondering if anyone else has had this, or if anyone knows what it might be?

The brakes still seem to work ok, so I hope it's nothing serious.