California building code has a minimum standard for noise transfer between floors which is at least 50 STC (sound transmission like voices, tv, etc) and at least 50 IIC (impact noise, people walking or jumping). 

Screen them, test them, replace them when you must, but build those core four people(Finder,PM,Contractor and Lender) and stick with them.For some of us this is our full-time job so we will do the heavy lifting if you allow us.  

Just make sure you set up your criteria to show to prospective tenants and than follow though with the screening.

Did you a do thorough tenant screening?

Single family homes in good areas are so much easier if you screen your tenant and put the right people in.

If the same due diligence of hiring a property management company is as detailed as buying another rental or screening the next tenant, you should be fine.   

Always screen applicants 2 months ahead of when your unit will be available.

Primarily the LTB has a policy not to evict so be very strict with you screen process. 

Many investors do not put carpet in their rentals and if you screen correctly,  some renters will stay for years.  

The key to successful MF investments seems to be in good screening of your tenants.