X-6 squared loud gearbox problem

[Jamie.T]

Hopefully someone here can point me in the rightdirection. The problem ive got is that the car makes a very, very loud high pitch sound when you rev it. Its the kind of noise when the wrong pitch pinion is meshed with a spur. (and yes i have checked that lol)

Ive slackened the slipper to try and it still makes the noise, ive stripped the gearbox and all the gears are meshing 100%, any ideas?
Thans in advance

Jamie......