What would cause a sulfur-like smell in your home after it rains?

Answer

Only a two cents opinion:

Quimical reactions in septic tanks.

When rain water gets into the tank its force quimically generate gases out to atmosphere. Considere look after a damaged pipe that links the septic tanks to atmosphere.

IMPORTANT:

Some of those gases do explode !!!

I had this same problem so I called a septic service and they chlorinated my entire system and thankfully have not had the problem since, and it's been about 4 years now.