R32 Gtr Whirring Noises With Full Lock Going Slow

[map7]

My car has just started making whirring noises. It happens only when I take off and usually when I'm turning. If I put the steering wheel in full lock to the right, then slowly take off in first gear I get a whirring noise followed by a loud clanking and banging from the front. I know enough that it sounds really bad and expensive.

I replaced the diff last year and my mechanic has been saying that the gearbox and transfer case is on it's way out. I can hear the main bearing, and I have this weird problem with when the front torque goes over 15% there is a slight banging like a diff is disengaging and reengaging.

My gut feel is that my front diff and the transfer case is stuffed but I would like a second opinion and if anyone could give me rough figures on how much it is to rebuild a gearbox with either standard parts or a good after market kit and fix the transfer case that would be great.