I hear a loud bang/pop from the dust bin when I turn the system on, is this normal?

Yes this sound is completely normal and not something you need to worry about. In fact it's a sign of a good, airtight seal and a strong suction force!

When the drum is empty, the flat metal surface on the top and bottom of the bin may flex a bit as the system powers on and creates a negative air pressure zone within the drum. This flexing is what creates that loud bang or popping noise. In some cases the suction force can be so strong that the dust bin connection hose may constrict and pull the drum slightly off of the ground, which can also create a noise when the system powers off and the drum touches the ground again.

In both instances, this will only happen with an empty container and the noise will go away as the bin is filled and the system is more frequently used.