Rangerover l322 suspension

Hi can anyone help I've got a 2004 rangerover td6.
This has Only happened over the last week,when I drive it my suspension goes down on the left front corner,when I park it up the suspension levels out back to normal,I've looked everywhere for an answer can't find a sausage,I've done a leak test took the battery terminal off over night,in the morning everything is normal,I go out and the same **** happens again the suspension works on the button no problem,the pump seems to be fine,apart from it making a bit of a load ish noise please can anyone put me in the right direction.
I'm totally baffled...
T.i.a.....