Clunk when cold?

Hi,

I've got a 2001 Mazda 323f 1.6 Petrol (new shape) (110, 000 miles). When I start it up from cold I get a loud clunk. It makes the noise sometimes as soon as it starts up or sometimes up to 2 minutes after its started, while I'm driving. I cant find anything loose and its fine all day long!

Starting with, clutch in or in neutral, doesn't seem to make any difference nor does moving steering wheel about (incase it power steering related) after starting and before clunk comes in!

Its very perplexing.

Any ideas?

Thanks