DIAGNOSIS: That's the classic sound of an airlock in the pump system. It happens when the machine is new or hasn't been used for a while, and the water path isn't primed.
FIX: You need to prime the pump. Fill the tank with fresh water. Take the portafilter out so there's no resistance. Turn the machine on and let it heat up for a minute. Then, with an empty cup under the brew head, turn the brew switch to the steam setting (the one with the steam icon) and let it run for about 30 seconds until a steady, strong stream of water comes out. Switch it back to the coffee setting and try a shot.
IF THAT DIDN'T WORK: Check that the water tank is pushed all the way in until it clicks. There's a sensor that won't let the pump engage if it doesn't think the tank is seated properly.
HEADS UP: Always do this priming routine with the portafilter removed. Trying to force it through a packed basket can damage the pump.