Any odd or new noises from an automatic transmission are, indeed, bad noises Gavin. Squealing or screeching from the gearbox can be caused by any number of things, but none of them are good and none of them are likely to go away on their own.
To be honest, I’ve heard of more problems with the Isuzu’s manual gearbox, with the fifth-gear synchro dragging and making a dry-bearing noise. The first thing I’d do is interrogate the car’s on-board computer to see if any fault codes show up and take it from there.
