If you think your office is too loud — e-mails pinging, elevators dinging, coffee slurping — it's actually probably too quiet. The trend in green building has made heating and cooling systems so efficient they've created another problem: silence. "It's so quiet you can hear a pin drop in some places," says David Sykes, who deals with acoustics issues for the American National Standards Institute. "That's too quiet." Studies link optimal noise — around 47 decibels — to productivity, and some are pushing for federal guidelines for "acoustical comfort." "A minimum amount of background noise is not only advisable but necessary," Sykes says. "But if it's quieter than that, people complain about it being noisy." Well, there's an app for that: Plug in an iPod to the ceiling pager system and play a track that sounds like air moving. The white noise might make you more comfortable in other ways, Sykes says: "If you turn it off, people start complaining about being too hot."