Lombard Effect

When we're in a noisy environment, and we're trying to communicate, it's only natural that we raise our voices.  However, this is apparently not just a voluntary thing-- there's also an involuntary reflex, called the Lombard Effect (or Lombard Reflex), named after Dr. Étienne Lombard, where your voice will automatically rise in volume even without a conscious decision.

This effect is not restricted to humans.  It has also been observed in birds, cats, and monkeys, just to name a few.  For example, see http://onlinelibrary.wiley.com/doi/10.1111/j.1460-9568.2006.04835.x/abstract;jsessionid=2C1EDED208F8B221BC66EEEFD8F6CBFB.d02t04-- if you dare.