if they don't fix it, it may be because the fan cable was not plugged back in completely when you put the case back together. This happened to me when I upgraded the RAM in my mini, and I had to open it back up to see what the problem was. If that is the case, your machine probably overheated over time. My fan would sound like it was running at top speed every time it was plugged in, but it was actually not making a complete connection to the power supply. That being said, I am not suggesting this is what happened, just offering a possible explanation. You may want to check and see if it is plugged all the way in before you bring it in, so they can't claim this is what happened.