mark Ransley wrote:

You have a bad wax ring, its leaking gas , I just had the same problem,
no leak on floor , but it smelled, the leak was such that the liquid
flows down , but gas leaks up. Your windows are oen in the summer, i
bet.

Mark is right. sigh
The wax ring can fail in such a way that there is no water leakge
but sewer gas escapes.
Jim