Exactly. There've been explanations offered. Other than the glug I've never seen a problem so I ignore it.
One of the few replies that may be worth something. These replies to posts have become attempts to be humorous. Thanks Holm.
While it is always possible it is not likely that you will discover that the fuel cap vent is malfunctioning. The temperature of the engine actually goes up for a while after the engine has been turned off. This residual heat radiates to other parts in close proximity to the engine, such as the fuel tank which sits directly above the engine, and is not quickly dissipated because there is no airflow as the motorcycle is stationary. This is referred to as heat soak. Some of the fuel in the section of the tank that is directly above the hot engine reaches a temperature where some of it turns in to an actual gas as opposed to remaining liquid gasoline. That gas bubble then rises to the top of the tank as it is now lighter than the liquid fuel. What you are hearing is that gas bubble dissipating in to the empty cavity above the liquid gasoline. This does not normally increase the pressure in the tank enough to cause the fuel cap vent valve to open. As the heat dissipates and the temperature drops no more gas bubbles are produced and the burping stops.
