Can one perceive an odour or smell it?
I perceive something is smelling.
I smell something.
I Perceive something is smelling.
Perceive essentially means your senses are registering something. You may or may not know if your senses are fooling you but you know what they are telling you. It also does not relate to your thoughts, opinions, or interpretation of your senses - think or believe is better in that case.
If you don't know where the smell is coming from, then trying to specify who/what the origin is with something sounds weird (but it's fine to believe or think that)- because a perception is typically something definite, but possibly limited. I perceive a smell, but not sure from where is better.