I think its a matter of assigning a sound source to an object. Not sure that a bell would be the best option though. How about a fog horn?
http://www.ci.norwood.ma.us/Email/Sounds/FogHorn.wav
http://www.madnessmansion.com/sounds/foghorn.wav
Once you convert the .WAV to .OGG, you'd need to hex edit the *.dsd file to let you attach the sound to the lighthouse. Not something I can help you with as I wasn't born with the ability to learn how to edit hex code. DD or one of the other Hex editing modders may be able to assist.