Sputtering or popping at idle speed is usually a sign of incomplete fuel vaporization.
This condition will not hurt anything......no need to worry.

The liquid fuel is pumped through vaporization tubes in the combustion chamber and is vaporized before being injected into the combustor. The fuel must be gaseous before combustion takes place. The sputtering or popping sound is that of very small fuel droplets burning or exploding.

When you send the engine to JetCat for service at the service interval, mention that you would like to have this problem rectified.