Noisy clutch bearing, noisy gearbox idler gear, noisy dual mass flywheel are all possibilities.
Nissan should have a record of the clutch slave issue.
First thing to do is to pop into your local Nissan garage and have a friendly chat.
If the noise is as bad as you say then they should have no problem identifying the cause and fixing it under warranty.
If your warranty claim is rejected then I have all the parts required.
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Cheers,
Alex.