Trek 1000 (2004) Headset replacement

There is a dreadful knocking noise and my headset appears to need replacing. Any reccomendations as it appears to be a non standard headset.
The trek website states "Aheadset, semi-cartridge, sealed"
Thanks

Seems rather young to be needing replacement. First make sure it isn't loose. www.parktool.com has the drill on how to adjust the headset. That's a pretty basic threadless headset. Something like a Cane Creek S-2 ought to work and be affordable.

I had the same problem with my Trek 2000 (2003). Took it back to the lbs twice. The second time they took the headset apart and pieced it together.
There was 1 piece that was slightly oval. They replaced it with a FSA, no charge. Problem solved.

Shouldnt that be under warranty?

I have a 2005 Trek 1000 so this question is important to me...