Started to get a Whining noise, which is fast getting louder. It sounds very much like the gearbox. The only thing that makes me doubt this is that you can still hear it when the car is in neutral, but i'm thinking that may just be because of the way the semi auto works?
Car has done 150,000miles...I'm thinking it maybe just needs the oil topping up?
when the car is in neutral some shafts in the gear box are still turning put car in gear foot on brake car stationery then nothing in the gear box will be turning.If you still hear the noise it isn't the gear box.If you the noise goes away it could possibly be a bearing I would check the oil level anyway and possibly drain the oil and check for metal filing or pieces of metal if you are sure that it is the gear box making the noise.Let me know how you go.