Yes, you can use virtually any .wav file, just needs to be the same name as the POI file, i.e. School_zone.GPX needs School_zone.WAV
I may sound a bit dim here but please bear with me. I have, on my Nuvi 310, added a wav file with exactly the same file name and added .wav to the file name. I still get the "ding ding" alert. Do i need to add .wav to the file or will this be recognised as the correct file type on install?