Then, she began to rudely complain that my industrial tenants were making noise that bothered her illegal tenants.

The rest is noise.

Complaints related to noise, parking, and guests are common in multifamily properties and can be easily addressed without going to such an extreme as serving a "Notice to Quit" or eviction.And what about Tenant C; is the third unit in the triplex occupied?

I am not sure how they enforce this (the city inspector asked during my latest inspection, but I only had people in my 4 bed unit so it wasn't an issue) I have discovered that the neighbors snitch, because of parking, noise, trash, etc. - even when you are within the permitted number of unrelated occupants :)

It's a real grind so you want to be in the investing business and not a bad debt collector.

So from what I understand they are saying landlord's should not enforce rules regarding unauthorized occupants, subletting, work on the property without conscent, noise complaints or general misconduct. 

I have had tenants living there since April 1st & I've had 3 major noise incidents happen in the last 30 days.

Is it a nice neighborhood with quiet neighbors and low street noise?

So, can they call the police on me if I am there working and they just don't want me there making noise?   

The state can make a lot of noise and scare as many landlords that they "are gunning for them" but their legal remedies are far more limited.