Not applicable to rockets
... could reduce noise a lot (IIRC -14dB is roughly 1/32 as loud) ...
Firstly: -14dB is NOT 1/32 as loud, it is about 1/3 as loud.
Secondly: With rockets, the bulk of the noise comes from the hypersonic airflow of the exhaust gasses slamming into the ambient air.
To ameliorate the noise of the rocket, you would need to fiddle with the boundary layer of the *whole* exhaust plume, where it exceeds the local speed-of-sound. This volume is typically many thousands of times bigger than the volume of the engine itself, indeed it is usually many times larger than the ENTIRE rocket being propelled.