Home update.
Since the water heater issue got seemingly resolved and no longer a factor, the other noises became more isolated.
As it turns out, there are two AC units that seem to be malfunctioning. When they're both off, there's no problem anymore. When they're both on, the place vibrates and at night it's unbearable.
One of the owners is willing to have the AC guy come out to check their unit. He's just been difficult to coordinate with. But since Saturday, he's had the system off.
The other owners are an old couple, and the husband told me he wakes up at 3:30 or 4 am every day to start his day, the exact fucking time things get really bad and I get woken up. When I talked to him on Saturday, he said he'd cooperate, plus he'd test things out and not turn on his system until 8 am. The result? The best (only) two consecutive nights of sleep I've had since December. My body was just so dead, it didn't want to leave the bed in the mornings, and I fell asleep twice during the day yesterday. That tired.
So I texted the old guy to thank him profusely and to tell him I'm trying to coordinate with the repair guy so stay tuned. He replied by saying they brought their own AC guy yesterday who says there's no problem with their system, so have a nice life. Holy shit, shared living is the worst. So now I have to find a way to nicely get the guy to agree to have the service guy check out his unit, and then if he has to repair or replace it, I don't know what's gonna happen.
The saga continues.