Thanks! That was a lot of help!

Yeah, I would definitely call it a drone now that you say that.
Basically, it's just a perfectly smooth rumble that resonates throughout his house when he starts it up in the garage. When he pulls up and sits in the driveway, you know he's home haha. But it's not annoying sounding, it's just super low and super smooth. It makes a car sound like it has power behind it, ya know?

Thanks again for all yalls help! Any further input will still be appreciated!