Is the extra dog noisy? 

Would you rather buy a building with 6 or 8 twenty year old, noisy, rusty furnaces or the same building with a newer cast iron boiler?

Sometimes gamers can be super noisy, even if they use headphones. 

Then they started calling and emailing us saying we needed to do something about our building because there were too many cars in the driveway and because on garbage day there’s too many garbage cans lined up on the road and because their snowmobiles are noisy...

He is noisy and obnoxious and leaves trash in the common areas.

Ants, raccoons, rats, noisy and messy birds like crows and ravens, hornets, yellow jackets.....Accent walls: hated them back in the early 2000's, still do. 

If there are noisy parties and they're bothering other tenants or neighbors, for instance.I had to disinvite a young couple who had a few warnings about parties in their unit, and the last straw was when one of their guests decided to pee out the bathroom window - through the window screen - and that window was in the middle of a U-shaped building, with their apartment in the inside of the U, and the other tenants who had windows facing the crazy party called me appalled. 

But they are also ugly, noisy, and expensive to run, so it depends a lot on the class of property and what your goals for the property are in terms of repositioning.It isn't always as simple as just slapping in a central unit; Electrical panel and/or service upgrades are sometimes needed, and you need attic or crawl access for duct work and returns, as well as a place for the air handler to go (which often means giving up a closet). 

I’m all for less turnover and happy tenants that don’t have to share a wall with noisy neighbors.

When you're dealing with small multifamily, the macro economic trends effect you a lot less.