But they are poorly looped, which is why the 'drone' thing (if I read the OP right, anyway).
There are many cars in GT5 with something extremely WRONG with their engine notes (or overall sound). And I don't just mean the sound used, but the playback of the sound. To many cars with repeating loops that have 'bumps' in the sound, sounds that are 'phase-y' (maybe that's the Pink Floyd reference?) cancellation between samples.
Sound just seems to be one of those things MUCH less important than modeling the detail in a car's headlamps in GT5. For the life of me, I can't understand why, though. You only ever see the minute detailing of headlamps in Photo Mode, but you LISTEN to the car 100% of the time you are driving.
This game seems utterly ADHD in so many ways...