As is true for all traffic laws, they are going to “target” minorities as yet another excuse to over police.
According to TFA, the law wasn't written to ensure that. It's selective enforcement, with cops making judgement calls both about how loud is loud and who looks like they deserve a ticket.
Anecdotally, in midtown, this isn’t true. (The Jersey plate correlation is.)
Keep in mind that making one’s vehicle flatulate isn't cheap.
Rusted out exhaust pipes from road salt in NYC on cars will make them louder but nothing like what I'm describing. Basically makes them have an annoying low pitched rumble similar to what those stupid $40 ricer 'fart can' modifications would. Few orders of magnitude of a difference between loudness.