Next week we will start the electrical system (100 amps sub-panel and redoing the driveway). 

If the problem persists, you could look into soundproofing options for the ceiling, like acoustic panels or even just thick rugs or blankets hung strategically.

Question to the apartment owners, management companies, single family portfolio investors and the like.Would installing solar panels on your income producing assets make sense if there was no upfront installation cost and you could "bill" the customer for electricity that the sun produces for each property?

I had 12 solar panels and a new roof installed.

There have been many different Electric panels over the years but for us these are of less concern as they are almost always very accessible and easy to swap out.

In an effort to further increase the energy efficiency of the property, I had 12 solar panels and a new roof installed.

I renovated the house to have energy efficient windows, doors, and energy source (solar panels).

If the current unit is electric you could have to replace the electric panel before going tankless.

Otherwise, you'd need to look at solar/off-grid (which has huge appeal on Airbnb, by the way).One other note is just to make sure you know the Airbnb laws wherever you're looking.

Are they showing you the roof, electric panel, crawl space?