Has anyone noticed an interference in their audio track while shooting with the HD7 caused by cell phones receiving a call?

I've heard this sound a couple of times while editing. It's a lot like like the sound of a bad mic connection, or the interference which can occur from a running microwave, if you've ever heard that. The latest time I heard it, someone on set mentioned a cell phone vibrating while it was occurring.

I didn't hear the actual cell phone in the audio track, but I heard this odd electrical buzz. I don't know if it was a coincidence, but as a precaution, I would suggest cell phones off, rather than on vibrate or even silent while shooting with the HD7.