Quiet hemi mufflers and cut outs for the street car.
The race car is a tough one. Race mufflers will not be nearly quiet enough.
Don't unload and drive it into the garage when you get home from the track at 1 or 2 AM.
Dry hops in the driveway or in front of the house are fun, don't do it! It leaves evidence behind.

Almost forgot. How loud are their lawn mower, weed wacker, leaf blower, snowblower? No need to be quieter than that.