As for lowering the fan speed, keep in mind that changing the internal temperature (and temperature differentials) can affect calibration accuracy, even though the components may still be well within their thermal specifications.
The 34410A specifies full rated accuracy in
ambient temperatures up to 55C. If you know you're not going to be using it within 25C of that temperature, there is no harm at all in slowing down the fan, as Agilent should have done. A variable-speed drive would have cost next to nothing and made the DMM
more stable over temperature, not less.
The 34410A is one of the examples I point to when I rant about how important it is for T&M engineers to eat their own dog food. Agilent's developers clearly never used the 34410A in-house. If they had, then (a) the fan noise would be tolerable; (b) the numeric display format would make it easier to distinguish between 120 mV and 120V; and (c) it wouldn't occasionally power up in the 1000V DC range for no reason.
Fortunately these gripes were all addressed in the 34461A.