You cannot perform any real estate services without a license. 

I learned the hard way.https://www.pabulletin.com/secure/data/vol28/28-44...

They have been my worst performing properties 10 years running, I sold 1 and thinking about selling the other. 

So I've obtained July and August rent in advance, and secured a larger deposit than normal. 

You have measurements of performance to determine if it's a good investment and then measurements of liquidity to determine if it is a safe investment.

I was told by the manager that HOA cannot do anything about it, but I know for sure that the air duct can be insolated and properly secured to minimize the noise and avoid wall vibrations.

I would definitely not refund June, and would treat security deposit as normal (use for actual damages). 

Constitution provides that "[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."

This feels like an even better situation to me  more security, etc.  

If the partners are not playing an active role in the management of the company and are purely contributing capital, than that falls under securities law and you'll need to file under RegD.