You can also adjust the Auto Acoustic Management on the Barracuda ATA IV to take about 10% off the seek times at the expense of a slight increase in noise. Seagate will replace your drive if you want to run RAID0, but the RAID0-optomized ones are a little slower in non-RAID situations. Here is more info on both topics:
RAID issue
AAM issue
I have a 'cuda IV in my home system and it's a trifle slow. What's interesting is that the Seagate Cheetah X15-36LP in my work system, running at 15000rpm, is very quiet too! Unlike the original X15 as mentioned by
EXman, the 36LP uses fluid bearings. Seeks are not inaudible, of course, but they're nothing like the bag-o'-microwave-popcorn sound of my old Quantum Atlas10k seeking. Anyway, Seagate is putting those fluid bearings to effective use in both areas.