Why is the dryer suddenly smelling like sewer water when I turn it on? This had not happened before. The clothes don't smell, it seems to be outside the dryer.

Wonder if a creature crawled in vent to keep warm. Do you have a cover on outside vent?

I just had an issue where my house would begin to smell like sewer gas when I turned the dryer on. Long story short, we had a plumber do a "smoke test" where they use a smoke bomb and a blower machine and blow the smoke into the sewer lines from outside. Needless to say, smoke poured out from under the toilets and from under the kitchen sink. The seals under the toilets were bad and under the sink as well. The dryer moves the most air in a house, even more than your a/c unit. I learned all of this the hard way, thankfully, we have a home warranty.