Do you get migraines? Don't quote me on this, but I'm pretty sure I read that though it's not common people can get olfactory hallucinations with migraines, and the most common smell is the smell of something hot or burning. Then again it could be something people often smell with olfactory hallucinations in general, too.

Also, the one time I went through a psychotic spell I had a lot of olfactory hallucinations. Then ever since, occasionally I'll get them, at seemingly random times even when I'm doing well mentally. It's this extremely odd smell that I can't even explain.