We have a sewer gas smell only in our bathrooms after a rain. We are on a septic and we keep it cleaned regularly. What could be the problem?

Your septic field may become briefly saturated after a rain and not allow sewer gas to escape into the field when your drains are used. I would check all toilets for a good seal on the wax ring and maybe rod the vent stack from the roof with enough rod to reach roof top to basement plus 20'. What do you mean cleaned regularly, a tank needs to be pumped once every 5-10 years.

Is there anything one can do to combat the smell or will we just have to live with it every time we have a heavy rain? All seals on the wax ring are good and the vent source is good. By regularly cleaning the septic I meant we just had it cleaned less than two years ago.