Well, since UDP is connectionless, you are going to have a heck of a time with traditional tools like that. My personal suggestion, is get wireshark, and set the filters to only deal with UDP, and only deal with the ports in question. Then run wireshark, and keep an eye on it.... when data is either sent to or received from the port, wireshark will show it to you, and I believe pretty much in all the layers of the OSI model (at least up to session and down to data-link). At the very least, this can help you see what information is being transmitted on these ports... which should help narrow down WHAT exactly you are dealing with.