Yes, sounds like an air lock, did you use the red pipe to prime the pump?
Make sure the mushroom cover on the water intake pipe in the clean tank is not pushed on to far as that has been a problem for me in the past, it just needs to pushed on a little bit. Also the little mushroom cover can easily get blocked with dirt so make sure it is clean. I would bet though that you have pushed it on too far.
I have also in the past when emptying the the clean tank of remaining water and left it running a little bit too long and the pump ran dry. When next using it there was more of an air lock than usual and on this occasion on speaking to Matt at Cleansmart he suggested lying the machine on its back (obviously) with no water in it, which will help bleed out the air lock, might need up to 30 mins.