strange noise

i recently got a 97 19tdsx 100bph with 85000 on the clock, it was going great until last week when a strange knocking noise from the engine came about when i started the car, it goes away after about 1 min but if u use any electrics or turn the steering it comes back but when u give it a rev it goes away, the car also heats up a bit and seems to be losing water, could all these be linked? any ideas