Photographer Tony Wu has a cool story up on his blog today. While shooting a large manta ray near Sri Lanka earlier this week, he was suddenly accosted by the normally-peaceful animal. The manta ray emitted a weird screeching noise as it headbutted him, telling him in no uncertain terms to back off. Tony swam away with what he jokingly calls "the first documented case of 'manta burn.'"
Tony describes the sound on his blog, but can't track down any documented reports of manta rays making any noise at all. Our own Explore section says mantas are sometimes "sociable with divers," though - perhaps Tony just got this one on an off day.