Disco gearbox about to fail?

My 2001 Discovery 4.0V8 ESi Auto has now covered 70k miles, and with little drama to date, other than the windscreen twice becoming loose and needing replacement. I have however become aware recently of some odd noises, I think coming from the gearbox. When changing up and down from first and second, usually when coasting to a stop, the car makes a strange 'twanging' type sound and sometimes you can feel a mechanical 'twang', as if a something is catching. It is also relectant to engage top gear until the car has reached around 50mph, and then when it does for a few seconds the car is reluctant to pull and feels almost like the engine is mis firing. All very odd. Anyone experienced anything similar? She has also started to make odd screaching noises at times when warm, these seem to be coming from under the passenger side of the dashboard...... and can be controlled by the throttle, accelerate a little and it disapears. All very strange! Similar experiences anyone, or any clues?.....

Many thanks!