First, if you have internal cables, pull on the housings where they enter/exit the frame. Next, take the pedals off, put a tiny amount of grease on the threads, and re-install. By "tiny amount" I mean a apply dab or two, then wipe it off using your finger. If that doesn't do it, pull the crank arms and BB. Put grease on the bb threads and re-install. Put a tiny amount of grease on the splines and re-install the arms (with a bit of grease on the bolt threads.) If all that doesn't work, do the same with the top bolt on the headset. You've already greased the handlebar clamp area? You can rule out the seat post if the sound happens when you're standing. If all that doesn't fix the problem, you can swap pedals with the Trek; and finally as a last resort, you can check your frame around the bottom bracket for imperfections in the paint that might indicate a crack.