This is for the '09 AT. I noticed this sometimes and I'm not sure if it means there's a problem of some sort. Say I leave my car parked overnight and it's cold by morning. I start it up to go to work in the morning, when I shift from park to reverse as soon as it's in reverse the tachometer jumps high and you hear the engine rev high for about a second and then everything drops back to what it was before and engine is no longer revving high. So it's a second-long "VROOM" with tachometer going up.

Also this has happened exactly once when I was parked after doing a drive for about ten minutes. I parked shut off the car. Then five minutes later started it up again and shifting into drive this time (not reverse) and it did the same thing. Normally this doesn't happen if the car has been used that day and it doesn't always happen every morning. When it does though I wonder what it is.