Urea doesn't smell like anything much. Leave it long enough and it breaks down to make ammonia, which does.

Most people can't taste it at all. And let's celebrate its 'invention' by the mammals so many million years ago as a brilliant solution to the problem of how to temporarily store and then excrete nitrogen in a harmless way as against the uric acid route used by birds and reptiles. People who have a test for the nasty H. pylori bug swallow a solution of urea and find it tasteless as far as I'm aware.

You mean like leave it under a hot mainframe?

Or expose it to warm temps in a lot of industrial processes?

It's a distinction without meaning, urea based products like DEF end up smelling like pee/ammonia. Laypeople usually specifically compare it to a cow urine smell