Forks popping...

[RBX QB]

Recent 12,000 service, which includes forks. It almost seems that there are air pockets in the forks which create a bit of a smacking noise on rapid bumps.

I can grab the front of the bike and bounce it real quick to recreate the noise. Are air pockets capable of this phenomenon?

[DarkStaR]

Make sure the fender is not hitting the fork tube.  Other than that... 

[CairnsDuc]

My knowledge is limited on the mystery that is Front forks, but it sounds like Cavitation.

I won't pretend to know how to fix it (Oil height a little low?)
But I would suggest take straight back to where the work was done and speak to them, or speak to a suspension specialist.

[Howie]

Since I can't hear the noise I can't say, and probably couldn't even if I did, but CairnsDuc has the right answer.