That doesn't sound like the Quantum I know. The hard drive shouldn't be so loud that it drowns out the sound of a stereo system. One thing you can try to do is to ask the sales rep. about the noise level. I'm pretty sure knowledgable reps. at places like LaCie would know this kind of infomation.
I don't think Quantum mechanism's are as quiet as they use to be, but they shouldn't be too loud. I have noticed that the 1.08 Gig IBM drive in my computer is significantly quieter than the Quantum drive.