Lag spikes every 1-3 seconds

I recently tried to use Photon Pun for our game, everything is wonderful except that there are lag spikes that happen every few seconds.
Ping is good and stable at under 30-80.
I thought it was game's problem and found that the Demo included in PunBasics-Tutorial has the same lag spikes.

I wounder if anyone knows whats going on and how to solve the problem.

Thanks

NanguaGames