You have to install a utility to do it, but yeah. The problem is ambient noise isn't that random in say, a data centre - it works better in a noisy environment like an office where you have people doing fairly random things rather then a whole bunch of oscillating fans.
I'd wager machine room fan noise has at last as much entropy, since office sounds are pretty structured and usually mostly quiet. In any case there's a significant amount of noise from the a/d conversion even when recording a predictable sound.
What utility is it?
On Ubuntu you can install the 'randomsound' package. There used to be a different one I used but I can't remember the name.
White noise is an enormous source of entropy, by definition. For example, take a stream of samples and record whether the least significant bit is 0 or 1. That'd be almost impossible to predict or influence from outside the system.