How to prime gammatone filters?
Mostly it depends on the kind of experiment you're doing. If you're interested in speech (as I was), most of the important information is in the 300-3000 Hz range, where low-frequency noise will have little effect unless it's extremely loud. If the experiment you're doing deals with static or other sounds with broad power spectra, then low frequency noise could have a significant effect.

As with most questions of perception, what matters most isn't really the signal itself but how the signal is changing. It's a big change to go from from silence to loud static. It's a lesser change to go from quiet static to loud static. That difference is more significant than the difference between going from silence to speech and going from quiet static to human speech, because speech is similar to neither silence nor static.