We have a terrible sewer smell in one area of our house that happens whenever we get a really hard rain. It seems to last only 15-20 minutes. We have it narrowed down to our basement storage area which houses our sump pump basin, furnace and hot water tank. The hot water tank and furnace are both new and the odor was noted before this purchase. We have a septic field which we had pumped and inspected already. I then had a radon system installed and they covered the other small drain hole also. That seemed to solve the problem for several months but after recent storms, the smell has returned. I bought a methane detector and it does seem to be coming from the sump basin. Could this happen if the drain tiles around our house need to be flushed? We live in a subdivision with street drains and part of the neighborhood is on a community sewer (starts 3 houses away). Could this be related? Any idea what I should do next? I’ve had multiple plumbers out with no resolution.
Thank you.

the simple thing to do is a peppermint test.
have someone go on the roof and pour a small bottle of peppermint oil down the main vent stack followed by a gallon or two of hot water.
that person shouldn't go back into the house for a while.
some one can now walk around the house trying to smell peppermint.