I bought a few of the Quantum LM drives back in the good ole Buy.com coupon days. I liked the speed of the drives (VERY fast), but they were the loudest IDE drives I have ever heard. They sound like a SCSI when seeking. I bought a 40 Gig Maxtor a few weeks ago that turned out to be a Quantum AS. This drive was for a coworkers PC I was upgrading. I was surprised on how loud it was. Not like the LM, but WAY louder than my 60GXP. The 60GXP is practically silent. I don't hear any noise at all when it's seeking. The Quantum AS still has the crunching Corn Flakes sound. The Quantum drives don't have a rotational whine sound like some other drives I've used. Its the noise they make while seeking that I hear. I haven't had a chance to check out a D740X yet, but Storage Review commented on it being noisy when seeking as well.
Noise is a personal preference kind of thing. My entire system is close to silent. The seeking noise of a HD is actually not all that bad to listen to. The noise is not constant, so its tolerable, but not preferred. A drive that has a rotational whine on the other hand, drives me up the wall. The Quantum drives fit into the former category. If you want a quiet drive, the IBM 60GXP, WD BB, and the new Seagate Barracuda IV are good bets.