I had a nasty creak and the LBS solved it as being in the seat post. Last month I had a group training ride on a rural asphalt bike trail after it had rained. The bike accumulated a lot of grit and wet tree needles that clumped together around the brakes. At one point I hit a large bump at speed, my left cleat broke, my foot flew off the pedal, and the sudden abrupt movements caused something inside my seat post to shimmy out of adjustment, making the saddle go up and down like a rocking chair. On my way home after the ride the LBS was still open, I stopped, and he fixed the seat post for me, but I hadn't been home to clean the bike, and some grit got inside the seat post, so on my next ride I got significant creaking noises. It was time for my 1,000 mile maintenance and new tires, so took the bike back, he redid the guts of the seat post and no more creaking. Hope this information is helpful.