PCARS sound is extremely enjoyable, unlike Gran Turismo which is quite literally all vacuum cleaners and annoying. However, PCARS isn't true to each car. While the sounds are good, they aren't very accurate for a lot of the cars. Heck some are just using modified samples from other models (and I'm talking about the finalized versions), when in fact that car has a unique engine note.
Example of in-accurate being the BMW Z4 GT3, it's got quite the sample, but listen to the real thing and its a bit more refined on the higher RPM's. The real Z4 GT3, isn't quite as harsh and actually inside is more transmission whine with a side dish of screaming V8. R3E is the only game to get it right the closest (with GT6 being the biggest epic fail of a engine of all time, seriously how did that get past QC?).
Example of a accurate-ish sample being the McLaren 12C GT3, because while not 100% bang on, its got the characteristics of the real car. The low-RPM turbo growl is essentially missing outside of pulling out of the pits though, which is disappointing. GRID: Autosport nailed it.
And finally an example of very authentic, the Audi IMSA Quattro 90. Which is like almost exactly like the real thing, one of the best examples of the 5-cylinder Turbo in any console game/one of the best all around.
At least though, aside from having many inaccuracies, the experience of driving isn't ruined. They still allow for immersion into the experience and feeling like you're driving a blood thirsty racecar, that wants to tear your bloody head off, or at least be thrashed around. So while inaccurate, they're still passable.