Originally Posted by woodcraft

I've seen that several times, with used tires. Sealant becomes sticky and glues the tube to itself.

Small pockets between the stuck sections burst on inflation- the pop that you heard. No fix, IMO, and a reason to not add sealant prophylactically, and to keep tires inflated if it has been added.

I've also seen glob of hardened sealant at the base of the stem, preventing tire from deflating.

Here's the remains of one: