Ya know, technically, it's not even a problem - it's just the sound of the fan spinning up or down. It is totally subjective if you think that it is a problem.
Yes, it's a problem.
I know what normal fan noise sounds like, be it Dell, Toshiba or Apple (little experience with fans outside of those makers), this ain't it (and the .mp3 provided earlier is fairly representative). As I said earlier, it's the sound of a motor rapidly engaging and disengaging at a higher RPM than it should hit. One possibility for the cause is that the fan is being overpowered, to an RPM above its design and shutting down because of that. Then the computer still needs cooling, so it starts the fan again.
A fan does not normally go from zero to max RPMs immediately and then cut off, then start up again and then cut off. As others have stated, noise issues aside,
that's not how fans work. Look at your ceiling fan, if you have one. Does it move air by rapidly spinning up and down, or is it a constant RPM?
I don't consider it a problem, and I'll gladly take a super thin MacBook that *might* moo once in a while under heavy load, or makes a barely discernable whine.
And IF those were the issues, you might have a good argument. People are referring to near-constant moos. My week 22 or 23 MBP, once it developed the whine, was constant and aggravating. It was at a pitch that cut through normal air-conditioner background noise, and when I worked in a near-silent atmosphere started to give me a headache in minutes.
A light moo is way better than the horrendous sounds other PC laptops make. So stop saying its a flaw, that's just your opinion.
I'm typing this on a borrowed 17" Core Duo Toshiba. It's cool to the touch, makes no noise aside from occasional fan noise and exhibits no whine.
It is ugly and it runs Windows rather than OS X. But aside from those two issues, it is a computer superior to MBPs and MBs in every single way (I could do with a matte screen, but c'est la vis). Too bad Windows is a deal breaker for me. I can live with ugly.
EDIT: I've held my ear up to every single laptop in this house (two PowerBook G4s, one MacBook Pro, one PowerBook G3, one iBook G3, one PowerBook 1400, five PowerBook 500s, and three PowerBook Duos) - and they ALL make some sort of whine noise when they are powered on.
If you put your ear up to it, yes.
The MB/MBP whine is heard from a distance and
is not normal. If you're unable to read, I'll explain it again: the whine did not exist for the first ten days of use. At all. Not a noise to be heard. Day 10, wake it up and get a headache.