There's a hum in the air... And I don't care for it.

Weird yet true story time.

I live in an apartment. There's 4 apartments on the north and south sides of the building, 2 upstairs and 2 downstairs.

About two months ago, my upstairs neighbor got a roommate of sorts. What is noteworthy is that we live in California, and the newbie's car plates are from Florida. First thought? They travelled three thousand miles to a Podunk rural town? Why? There's better opportunities in other towns and cities than this one.... But this isn't the first out of state plate to make themselves comfy here, in this complex which forbids subletting.

Anywhoo, two weeks ago, upstairs neighbor goes away-- her red car hasn't been back. Mr Florida plates gets a new temporary roommate; older man with a white truck that needs a tune-up, Cali plates.

Since that new person made himself comfy, there's been a buzzing/humming sound which permeates my apartment. For the most part, it's much like if one turned their subwoofer waaaay up; low in tone but definitely there, rumbling away.

Last night, it was stronger, more irritating. As in, sitting on the couch and feeling it vibrate.

Normally, it's not so noticable.

Last night, the truck drove off, and a white sedan has taken it's place, next to Mr Florida's Honda.

I'm not making accusations, merely noting my observations.

I find it weird that the upstairs neighbor I've had for over a year pulls a Houdini, and now strangers come and go, playing musical cars, at all hours of the day. Other than that, upstairs is pretty quiet, except for boot-enhanced footfalls from people walking around.

I find it weird that apps can document the low frequency rumblings my kids don't hear/feel.

Now, I've read about dissenters being targeted with Sonic/low frequency as a means to harrass them into capitulation. I don't know if that's the case, but I do wonder and prepare appropriately.

Thoughts?