The Mini has developed a gearbox noise over the last few weeks. It's louder when the engine is warm and manifests itself as a low pitched whine when backing off the accelerator in 2nd, 3rd and 4th. It's present but much quieter when rolling in neutral. Under acceleration there's no noise.
Does anyone have a suggestion as to what it might be? I'll be pulling the engine out to repair the problem but it would be nice to have an idea as to what it might be.