super works 2hp compressor

i'm hoping someone out there owns one of these, i bought one just for pumping up tyres so i can move around, i already have a big one for everything else, but this one i got of ebay 2nd hand and i find it operation a little funny , it works but i suspect the pressure switch might be playing up, so when i power it up it the motor runs and fills the tank then does a pressure release and must come back down to a set pressure,(i would expect the motor to be off at this stage when it's full) but there is a funny noise as if the motor is turning ultra slow, but when i use the air in the tank the motor kicks in a again as you would expect to fill it back up, also the other thing is if i hit the off button all the air is let out of the tank through the pressure switch till the tank is empty ????????