Too much pressure

Hi,

I am in Aspen for the summer from NYC and I wonder if this problem is altitude related... When I press the brew button, there is a rush of water coming out in an uncontrolled manner. after a few blank shots, it returns to a normal stream, but then it starts again. It ruins my shots a lot and it's hard to predict when it's going to happen again. The machine is out of warranty and I am wondering if this is some kind of adjustment that I can do if I open it up myself...

Thanks