I don't remember reading anything about this in the past, so I thought I'd throw this open to see if anybody has any info or advice.
Ever since I bought this VR4 I've been getting intermittent problems with the AYC diff making low sounding grinding/droning/graunching noises. Within in a week of getting it I had both the AYC fluid and diff gear oils changed which seemed to cure the problem for a while, but in the past few months the noise has become ever present, but far, far worse on left handers than on right handers, and ONLY when the AYC lights are on.
The old car started making a higher pitched whine last Easter and I assumed that to be the brake discs. Sure enough, once I swapped the discs over to the new car, the same noise transferred over as well. Unfortuantely there's also this much lower grinding noise on the new car that was occurring before I swapped the discs over.
I've just come back from Mitsy who've done me a free oil change on the diff as they drained it and found it to be BLACK (this is after 5000 miles). Sadly it's still not solved the problem as I get the same horrible noise when doing sharp or long constant radius left turns with power applied (just enough to get one bar, so 15-20mph is enough!)
I'm convinced that there's something wrong with the diff itself, as the AYC pump appears to be working fine. To further this assumption (and to differentiate it from the possibility of it being the drilled grooves of the brakediscs rubbing against the pads, which is what I think the higher pitched noise is), when I drive in the snow at 5mph in straight line and stab the throttle, i.e. so you get all AYC bars lit up momentarily, the same horrible low pitched grinding noise appears.
Can anybody shed any light on this, or has anybody ever experienced anything remotely similar? I'm convinced my diff is knackered.