Switching to lower voltage?

Hi all... I have a fan rated at 5V/260mA that I want to undervolt so it runs quieter (this is for an overclocked RPi; thus far my measured temperatures indicate that I don't really require a fan, but I want to have a little extra thermal headroom "just in case").

I tried running the fan off a 3.3V supply, but that doesn't seem to have enough juice to start the fan from a standstill. I wired a 3.3V and 5V supply both to the fan with a DPDT switch, and once the fan gets started off the 5V, I can flip it to 3.3V and it runs just fine... so this brings me to my idea:

1) Can I build some sort of circuit that would run the full 5V to the fan, then after about a second, switch to a "reduced" supply?
2) Would 2x 1N4001 (series) be sufficient to provide the "reduced" supply for this fan? IIRC the voltage drop on a single diode is ~0.7V, so two in series should give me 5.0V-1.4V=3.6V, correct?
3) If the diode design isn't a good idea for achieving the desired voltage, what's the simplest way to get about 3.3 ≤ V < 4.0 ?

Since the diodes are rated 1A, the 260mA should be fine (and don't motors draw less current when they're working below their rated voltage), and the fan's datasheet actually lists its operating current as 160mA so I'm guessing the sticker rating of 260mA is for startup draw (which the diodes wouldn't see).

It wont be the voltage stopping the fan from starting it will be the current. You probably want to boost the current to get the fan started and then just switch to the 3.3v.

My idea would be to put an inductor and a diode in series with the fan. use a 555 mono-stable timer to short the inductor to ground for a short time at start up and then release. (must like a boost circuit)
This would give you a extra boost of current through the motor at start up, .... I think

How about this?

Alec_t,
I like your idea of starting the fan at full voltage and slowly dropping back. (at least that is what I do)

In most cases like this the prefered method of fan speed control is PWM.
There are off the shelf kits for computer fans, some as low as $2 last time I looked.