Chris, yes there are several causes that may produce "solder splashes or
solder balls" during wave soldering. Before one can answer, you have to
gather the following information: 

1. What type of board you are soldering? PIH only or a hybrid of PIH & SMT.
2. Board thickness and via size(s)
3. Where do you see the splshes, Front, back or both, Leading edge or
trailing edge,
    near the PTH or all over.
4. What is the pattern to these splashes?
5. What type of solder mask is on the board?
6. Physical shape of the splashes.
7. Do these solder splashes easily knock off or not?
8. Soldering process parameters.
9.Have you try to run just the raw board without components?
10. What quality plating is in the PTH? Thickness, voids etc.
11. Are these boards HASL or OSP finish?
12.What type of flux, noclean or standard water washable?

Call me if you like to discuss further.

Pratap Singh
RAMP Labs
(512) 255-6820