Who knew? According to Snowflakes in Hell a ship was able to dissuade Somali pirates from boarding. How? Well:
Somali pirates attacked the Maersk Alabama on Wednesday for the second time in seven months and were thwarted by private guards on board the U.S.-flagged ship who fired off guns and a high-decibel noise device.
I have to agree with Sebastian on this one, I think the noise makers had little to do with fighting off the Mongol Somali hoards. Something tells me they were more afraid of being killed by bullets than discomforted by loud noise.