I went to start my car this morning and the battery was flat, I jump started the car and when I got to work and turned the car off I noticed that there was a buzzing coming from the engine bay even when I locked the car.

I opened the bonnet and it seems to be coming from the ABS pump.

I have been having ABS problems lately, the car drives fine then all of a sudden I get the "DSC inactive" with all 3 lights coming on, it will not change gears and I have to manual shift using triptronic.

I had the car scanned and it came up with "Pressure Sensor (Offset)" under the ABS scan, I cleared all the codes and the error came back but once I re-scanned again the error changed to "Pressure Sensor, open circuit".

Does this mean I need to replace the ABS pressure sensor?

I don't think it would be the ABS module, it was playing up last year and after some help with people on this forum I ended up having the module re-built and the car has driven fine since then, also that was a different problem (Car not changing gears at all and going into transmission fail-safe mode)