There must be some sort of fan control device in my PSU even if I didn't see one, for the whine of the fan certainly changes in amplitude depending on load. It could indeed be that the bearing is shot and exhibiting the exact behavior you mention. I have heard that a PWM circuit can also cause unnatural modulations in the fan coils, which might also cause a whine. Whatever the cause, all I know is, this fan has to go.
Also, after stopping all the fans in my system except for the other 92mm fan in my PSU there is a sort of "rattling" noise going on in my system, indicating that that fan might be on its way to the graveyard too.
What I plan to do is take out the 92mm fan, tape up that vent, and replace the 80mm unit with the 18CFM NMB fan so that the air will be pulled in from the back and flow directly across the components in the PSU. I will also have another 18CFM case fan exhausting air from the back, and will replace my current Volcano 7+ heatsink, which exhibits some fan vibrations and is quite loud even on "low", with an Artic Cooling Super Silent 4 TC. Additionally I have already unplugged my Radeon 8500's wimpy fan (doing fine so far with the airflow of the exhaust fan over it) and have a Maxtor FDB HD, whose noisefloor is nearly that of the Barracuda IV (that is to say, nearly inaudible, even in standard mounting configuration). How does this setup sound to you?
Just to get some thoughts jumbling around in my head down...
First, what is the "static pressure" measurement for fans? And which is better, higher or lower? (in terms of airflow/noise) For example, the L1A has a SPR of 1.57mm-H20, while the NMB has a SPR of 0.07in-H20.
Second, my PSU seems to have especially small heatsinks. Would this be a major problem if I used a low CFM fan?
Lastly, should I leave the bottom 92mm fan vent open or closed (in regards to CPU/PSU temperature) considering that the back vents are quite small?