We had been trying to find the source of Al's creaking for weeks. He had first brought his M2 in to have the bottom bracket replaced, since he thought that was the source of the creak. The bottom bracket seemed fine, so I reinstalled it with plenty of grease on the threads. Cartridge bottom brackets will often creak if the threads are dry.
It still made the noise. We checked the chainring bolts, the crank bolts and the seatpost clamp bolt. I pulled the seatpost and regreased it. No go.
Over the course of about three weeks, I either removed nd reinstalled, adjusted or replaced every component on that damn bike. The problem was, I could never make it creak. I would test ride it, and it would be normal. Al would get on it, and the creaking would start.
Keep in mind, Al was 3 inches taller and 50 pounds heavier than I was.
Finally, as I was once again checking the cranks, I saw it. The paint had a telltale flake missing at the downtube/seattube junction. I used the Park Tools frame straightener as a cheater bar on the crank and pushed it sideways.
A crack opened up at the edge of the weld, just enough to see it.
I've never been so glad to see a broken frame. At last, I had an answer to the mystery creak!
Specialized warrantied the frame, and Al was happy. I was happy as well. I had become way more intimately acquainted with that bike than I ever wanted to.