Just recently had the 190,000km service done on my 2016 Isuzu MU-X and just started to take notice of a squealing/screeching noise just after a gear change happens or when I’m opting to use manual mode. At first I thought it was a suspension noise, but then I started to make it happen and controlled when it happened by selecting gears in manual or auto. This would not happen every gear shift, but in a random way. I am concerned that there is a problem brewing.
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.