I've had a few Canon DSLRs, one being the Canon Rebel XT. It does have a distinctive sound, one that I could pick out of a blind lineup against other Canon DSLRs.

The biggest reason that it is louder is that it was a very early model in the entry level digital SLR camera arena. The Canon Digital Rebel was the only other predecessor in the line. Therefore Canon simply didn't have much experience in this mostly plastic body production. Along the same lines, adding in the additional hardware necessary to keep it quiet was likely low on the list of important features in such an early low end model.

Since then, many models have come out with special silent shooting modes. These really take the sound dampening to a new level and are a great reason to upgrade if you need this feature. I have found the modes very useful when in a Church or similar situation.

How can you quiet it? Really you have very few options. The one I will suggest is to use mirror lockup if the Rebel XT has it(sorry I don't remember off hand). This will keep the mirror up but obstruct your view, not necessarily reducing the noise, but letting you control the noise at least.

See these other questions for more detail on this topic:

• What makes sound in a DSLR camera?
• What's the difference between Canon's silent and non-silent shooting?