another rear diff mount

i have a noise in rear that sounds like sway bar bushings.. thisonly happen when clutch is engaged slowly rolling through parking lot.. press in clutch and noise goes away. just sounds like rubber against metal squeak.. i looked under the car today and noticed the diff raised slightly off the curved part of the diff mount.. here is a pic of how much daylight i can see through.. mount seems to be tight as per placing jack under.. please help !!!

78 280z