Here’s some advice I read about in the Hot Tips section of the Harmony Central newsletter:
Turn Off Your Cell Phone
You probably know to turn off yourduring a session—the last thing you want is some weird ringtone intruding on a killer acoustic recording. But you may need to go even further and actually take out the battery. When cell phones update, and sometimes when they receive a call, they may generate “hash” that can get into signal processors, amps, pickups, and other electronics found in the typical studio. What’s worse is that this may be recorded without your actually hearing it, until you play back the recording. So, if you’re involved in a crucial session—particularly if it’s a live recording—you can probably do without your cell phone for a bit if removing the battery ensures you won’t get any nasty interference.