[05SDI]

I too have heard this sound when starting our cars (both of them) when the weather is cold. In my car I switched to synthetic oil the very first oil change (yes I know some feel synthetic oils should not be used during break in) and have ran it since then changing every 2500 miles whether it is needed that often or not.
BUT to ease you mind some:
Last winter when we had about 8000 miles on my car, one very cold morning (about -32 F) I went and started my car and as soon as it fired up it immediately reved to 6200 rpm and bounced off the rev limiter for about 5 or 6 seconds!!!! It was very cold so I didn’t get in the car to start it I just reached in and turned the key. After jumping in and shutting it down, I spent 10 minutes looking for things wrong under the hood and for fluid running out on the ground. After checking things out inside the car I was ‘sick’ when I found that the heavy duty floor mat I had put in there to keep the stock ones from getting ruined must have shifted as I got out the night before I must have moved it so it pushed the accelerator pedal all the way to the floor!!! I was so bummed that a $15 floor mat might have cost me BIG $ for a new motor! (assuming warranty doesn’t cover being dumb!) Well the car now has over 22K miles on it and I have found NO ill affects due to this mishap.
Bottom line don’t let the sound bother you!
05SDI