Somebody here is bound to be an expert on this random topic, so here goes...
For the last month or 2, when shifting my 2010 base w/ AT from park into reverse, I will often hear an audible "beep" inside the cabin. it is not the same beeping noise as say, the seatbelt alarm. it is quieter and of a lower tone. i get a single beep, then nothing. it doesn't happen all the time-maybe 2 out of every 3 times. it only seems to happen just after startup, and only when going from park to reverse. nothing if i go from park to D, and nothing after i back out of my driveway or parking spot and into D. no other symptoms or driveability issues.
car is at about 65,xxx miles and has never had any significant drivetrain service. i'm thinking about a trans drain/fill next summer. fluid level was fine when i last checked, but i'll admit that was a while ago.
i know that these cars are totally beepalicious. this is the first with an indeterminate source.