I've had the same sort of problem twice. Once, tightening up the bolt holding the saddle to the seatpost stopped the creak. The second time, dirt had got between the seatpost and seat tube. Make sure you've cleaned and greased the seatpost and that all your bolts are tight.

Also, carbon sometimes just creaks.

You generally don't lubricate a carbon seatpost. This makes it very difficult to tighten the seat clamp in the frame properly. The easiest thing to do if you have extra parts is to swap out that seatpost and seat with an older one, and see if the sound stays.

Could be the rails themselves. Check there's no hard wear on this. I've seen this on saddles with carbon rails or older Ti ones. Plus loosen off all bolts, strip, grease and reassemble. Check the inside of the seatube as well....

I have the same setup, though a different saddle. Tightening up the bolt that holds the saddle usually does the trick.

I am really getting skeptical of these super light weight parts in my old age.

thanks for the replies. There's no grease on the seat-tube where the post goes in. The carbon post was cheaper than the thompson I was after, and I think I'm going to pick a thompson up as this one has too much layback for my liking.

Everything is tightened down, but I'll go over all the bolts again tomorrow and double check it all.

Cheers,

J.

I know it will depend on the material used for both seat tube and seatpost, but greasing is important in order to avoid getting the seatpost stuck in your frame. From sheldonbrown.com:

"To update an old saying, 28 grams of prevention are worth 454 grams of cure. Stuck seatposts are always the result of improper installation. If you do it right, you will never have a seatpost get stuck after you install it.

1. Always use grease. The inside of the seat tube should be heavily coated with grease all the way 'round before you install the seatpost. If you use enough grease in the seat tube, there is no need to grease the seatpost itself. (When you make a peanut butter sandwich, you only need to put the peanut butter on one of the slices of bread.) "

In my experiance, as well as stopping the seatpost sticking, grease can also prevent creaking.

Sheldon's website is a great source of data but he's has a lot more experience with practical materials, not carbon.

http://www.velonews.com/tech/report/articles/8835.0.html
From Easton:
No grease on carbon posts. Grease contains certain minerals that can attack clear coats, can penetrate the resin matrix and could cause swelling of the composite laminate. Can you say "stuck seat post?" Don't use grease.
John G. Harrington
Vice president, bicycle products
Easton Sports, Inc.

From Campagnolo:
No grease. In some cases it can be dangerous to use grease as the chemical composition can cause a reaction between materials. Besides, it increases the torque required to clamp the post.
Richard Storino
Campagnolo USA

From Deda:
Absolutely no grease on carbon, ever. Also, do not use solvents to get old grease off, or to get old grease out of the seat tube. John Harrington of Easton and I believe that many solvent residues in the seat tube soften the gel coat of the carbon, then bond the gel coat to the inside of the seat tube, freezing the seat post in position for eternity.
Tom Franges
Deda Elementi North America tech support

From Bontrager:
There are some petroleum greases that are slightly acidic. That acidity can attack the resin used in carbon-fiber construction (frames or posts). This same acidity can attack aluminum or steel frames components, too. However, most greases are engineered to be slightly basic. Neither Trek's nor Bontrager's carbon resin is affected by this acidity. The main reason we suggest you don't use grease on any seatpost inserted into a Trek OCLV frame is that there is not enough surface roughness inside the seat tube to ensure your post stays where you put it.
Scott Daubert
Trek team liaison

seat tube is clean, yes? on my mtb if dirt/sand gets into the seat post it creaks.

OBESITY

My fat ass?

My saddle itself had a squeak this season--- I finally fixed it by rubbing a bunch of Assos chamois cream between the leather sides of the saddle and the plastic cover that was partially supporting the saddle. That stuff did a nice job of reconditioning the leather as well.

-Marc