serotta

I have a Bontrager seatpost that has been on the bike since build up. The bike has had a creaking noise since build. I've reinstalled BB, crank, bars, wheels and pedals to no avail. Today, I pulled the seatpost and seat then used an old UNO with seat attached I had on the shelf. Like magic the creak disappeared. I installed the orginal seat, and the creak was still gone. The Bonty post has been lubed, tightened, etc. many times, but the creak appears to be part of the seatpost to seat attachment point.
Has anyone else had or heard of this problem?