Had the WCW backpack for 18 months now and been fine...up til now! Yesterday I had to come home early as it packed up (thought it was just battery gone). But charged it last night and still doing the same today. It's ok for about 30 secs, and then it just gets slower and slower til it just comes out a dribble. Sounds like the pump is struggling. Opened it up, no obvious problem. Does this sound like a pump problem? Anyone else had this?