Well, nothing stops you, or other teams for having a separate "noise" tune/engine map.
Also the RPM defined by piston speed means that whatever happens at speeds higher than the tested ones, is "fair game".
Well, with a turbo, you might even set your competition rev limiter lower than the noise test RPM.... But still fail noise.
And remember all the dbA, dbC noise filtering stuff. Did you have the correct setting at your db Meter?