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I think you're referring to "Jake Braking", which is very noisy and is banned in many towns (in California).

"Jake Braking" is similar, but pertains more to diesel engines which have a special valve to support this since they work differently.

Engine braking on a gasoline engine is actually quieter than normal operation.

At least the manufacturers of those products assert that correctly installed ones are no louder than the diesel engine in normal operation.