Does a restrictor plate impact the noise generated by stock cars?

Not noticeably. The reason the cars sound different is because the cars use 180 degree exhaust. It was first introduced for the 1995 Daytona 500 by the Morgan McClure Team. They won the race with Sterling Marlin as their driver. Everyone was curious as to the odd sound the car made as it raced around the track. The exhaust was available to everyone the next year.

Yes it does. The restrictor plate "restricts" the air from going into the car, so the car does sound a bit different. The engine's power is reduced causing it to sound and perform a bit less. This prevents the cars from going too fast.

No. It's just as loud turning 8000 rpms as it is 9000 rpms. The pitch of the engine is just slightly different.

yes?