Okay, just to explain, Sonic, Tails, Knuckles, and Amy are all living in one large house they bought together.
They're nudists though, obviously, so while they're at home or at the beach, they're naked, which is how we see them ('Cept Amy) in the video games. They have a car, but they don't take it to the beach, 'cause it's so close to their house, they just walk freely to and from the beach whenever they want. Amy is a bit less frequent to the beach, thus Sonic's backrubs are usually a rare treat. Unfortunately, the law requires the males to wear shorts, the females, shorts and shirt, when on the streets to or from the beach. However sometimes late at night they'll go straight to the beach for a late night skinny dip in the cool water, not bothering to bring clothes. It really brings the four close together as friends. (I might add one of those get-togethers later in the story. ;D)
They also don't worry about THINGS LIKE male backrubs, cause it's all good friendship stuff. Sonic is only surprised at Tails' question, cause Amy already gave him one.
So, I hope this satisfied you need to get hot and bothered. ^^ Part 2 on its way. And I'm not giving up on the TMNT stories. I'm just interspersing them a little.
Oh! And no offense to any nudists that read this. I respect you guys a lot!