I have a giotto prem. 2 years old and i decided to check the pressure so i bought Portafilter Pressure Gauge Kit, i noticed the reading will go up to 11-12 then it stay there for a second or so then it will drop back to 4 or so then it will build up again? it sound like the pump shuts off or at least the noise while quiet when it reach top pressure? is this normal ? if i remember i did test it a while back and when it reach 11-12 the pump will keep running and the pressure will stay their for a while? am not sure what is the right way for it? please help

In vibe pumps, flow and pressure are inversely related. So the noise situation is simple -- High pressure => Low flow => Quiet operation.

The drop to 4 bar is more puzzling. Basically something opened up to release the pressure. If you didn't get water leaking out of the portafilter, the most likely culprit is an OPV opening up, with the water discharging either back into the tank or the drip tray; the other possibility is a leak out of the three way valve, with the water discharging out of the bottom of the group.

If you don't know what an OPV is, search the site and FAQ, there's lots of posts.