There are usually two solutions to this problem.
1. Its the drain sucking air. This is easy to solve. Just put a small hole in the drain to allow the drain to "breathe." that should solve the problem.
2. Its the drain (where the water actually leaves the drain pipe) gurgling. Pretty easy to solve as well. You can get a pvc
fitting that has a turn valve on it. The valve should turn from the vertical to the lateral position (fully open to fully closed). If you turn it just a little, it should close off the valve just enough to keep it from gurgling. Thats what I did...working great.