Argh
That's usually something slipping, and that is usually the front broken off the front clutch drum.
Assuming you don't fancy a full rebuild, replacing the clutch drum is DIY'able if you're able to get the gearbox out. Its available new from ZF dealers, or you could use a donor gearbox, although that's a risk that it also has a cracked drum. Prestige have a dead one in at the moment I think, although I don't recall what the fault was.