MY ZT-T does this as well, under load in first gear on pull off or in reverse. I have been told by numorous people that it is nothing to be too worried about, probably the clutch release bearing or the clutch plate.
The guy I spoke to at MGR Direct in Longbridge last week said that many 75s / ZTs did this and it would not cause the clutch to go any earlier then it will go anyway. Whether this is 100% accurate we'll have to wait and see.
When the garage checked it out and I informed that I have warranty, they advised that it may be release bearing or clutch plate but to find out for sure the clutch would have to be strpped down and if the warranty would not cough I was left with the bill, so I passed.