Our master bathroom sink is gurgling. What is the problem and what should we do?

It could be air pockets in the water as it travels through the pipes, having venting installed could help, pending that there aren't any clogs.

When you hear "gurgling" from a trap it means that the system is trying to vent. The water from your flush is racing down the pipe creation a suction. If the vent is blocked or improperly installed the rush of water pulls air through the trap in the lavatory. Hence, your gurgle. The solution is to snake out the lavatory roof vent. Put out enough cable to reach the base and 15 feet more. When you're done flush the line with hot water. Hope this helps and good luck. TOM