5400 rpm drives are normally less noisy than 7200 rpm drives.
I currently have a seagate monumentus 500gb. Its not the XT version. I wouldn't buy this drive a second time. My first one failed after 6 months. I had to RMA it to seagate and it was expensive to do so. Seagate charges 20 bucks just to send you the drive first, where you return your old drive in thier packaging. Western digital does this for free fyi.
With the exception of Samsung Spinpoint F3 3.5 in drives (nothing even comes close in speed to these bad boys) every drive i buy now is a western digital due to their return policy.