Originally Posted by
gotdurt
My Specialized Stumpjumper did that. There are internal lugs in the frame that twist in the tubes when you apply enough torque. Specialized recommends pouring linseed oil in the tubes (tilt it so that it penetrates the offending lugs, in my case where the top and down tubes meet the headtube). I have to do it about once a year.
BTW, I forgot to mention how to check this... first try holding the seat in one hand and the handlebar or stem in the other, then push/pull them in opposite directions, as hard as you can (torque is key). If it creaks, the frame is likely the culprit. If you can't get enough torque that way, try straddling the bike (drop the seat) with the frame pinched between the knees and your hands on the bars, then try to twist the frame.