Keep coming out of what?
IPX is Novell's old protocol. If you have any old print servers (think HP Lasers with Ethernet interfaces), that's your most likely source.
Other possibilities: Fax servers, older Microsoft servers (~NT, early Win2K) set up by n00bs.
Aside from being a little verbose, it shouldn't hurt anything.
If anything netbios would ride on top of IPX (Novell's Netbios was better than IBM's for most stuff, and you could shut it down without killing the stack) much like it can ride on top of IP now.
Good Luck
Scott