I hear the noise I think you're describing, although I'd call it more of a servo or pump noise than power antenna motor, and I've had my 2K3 from new (70k currently). Admittedly, mine does seem to be getting more noticeable, but it's been unusually cold (by our standards) for the past two months and I've also been spending more time with the radio off lately so it could just be I'm noticing it more.
I would also check the power steering fluid reservoir. Mine's been sitting at the cold-min line for since before I started noticing the noise becoming more frequent, but I've been too lazy to do something about it. Finally picked up a bottle of Dex ATF the other night and plan on doing a turkey baster drain-n-fill until the quart is used up. Even if it's not the source of the noise, it'll make me feel better to get some new fluid in there.
-Brent