Nasty sweet smell in bathroom - Dead rat in walls?

[notting0]

Did you ever find out what it was because I have the same smell. Year 3 it only starts when the temperature starts cooling, only in one room bedroom with small bathroom. With same smell as you described driving me nuts, my husband can't smell it which I don't understand

[peabodyn]

Dead mice do have a sweet / ammonia kind of smell. It takes a while but the stench will subside.

[tamajane]

We had a sick sweet smell from the wall/floor that wasn't going away, it was rodent waste that had saturated into some insulation and wood. Looks like they had a party in there. Smell would reappear depending on the temperature and humidity. Had to open the wall and replace.

[Parnassia]

Originally Posted by notting0

Did you ever find out what it was because I have the same smell. Year 3 it only starts when the temperature starts cooling, only in one room bedroom with small bathroom. With same smell as you described driving me nuts, my husband can't smell it which I don't understand

Another possibility is a small colony of bats. They are often attracted to heated buildings in colder months and can squeeze through really tiny crevices to get access to the inside of walls, attics or crawlspaces. Their guano can have a sweetish odor. A professional can inspect the outside of the house and find evidence and entry points. There's no reason to exterminate them...there are humane ways to evict them.