Can anyone tell me if there is a significant difference in sound between, say, a Class 24/0, a class 25/1 and a Class 25/3, or do they all make more-or-less the same noises.
They are all basically identical, its the same basic engine in all 3 of them, just a few minor tweeks to get a bit more power out of them in the 25s over the 24
Yeah, I agree with Richard's assessment. Worth noting that the extra power was gained by increasing the speed of the engine, which would have negligible effect on the perceived sound, unless running flat out.