After a bounce of IP addresses this morning, the server is being bombarded with requests to port 11326 from all over (192 different IP addresses and counting). 4616 requests in two and a half hours. A google search on what might be lurking at port 11326 doesn't reveal the problem, though there is the possibility it is associated with the OpenPBX/CallWeaver program.
6 hours have passed since the initial post and it's up to 703 IP addresses making 12726 requests.
UPDATE 2: 5:45pm
Finally set up a netcat on the port to do ...