1. A very slight but noticeable whine from the DCT is normal but it should not have come only after your 1200 mi service
2. The 1200 mi service is not a "DCT service", it is an engine fluid and other fluids replacement.
3. I expect there is nearly a zero chance that they mistakenly changed your DCT fluid but it did happen to quite a few cars and most got the wrong fluid and had serious tranny problems that resulting in them being replaced. Double check with your dealer on this.