I too have had periodic smells that just drove me nuts. Always bad ones, it seems, lucky me. I've been through bouts with smelling dog poo everywhere even when the dogs are clean and not the source. Nobody else smells it. I went through a phase where any heat on my face (dishwasher/oven) evoked the smell of black pepper and sneezing. Quite often burning smells like plastic, electrical(scary), smoke(from fire and cigarettes) which nobody else smelled. I am very allergic to cigarettes so my body reacts by vomiting and getting a migraine even when I can't smell actual cigarettes AND when I smell these phantom ciggies. So I know it's not a mental reaction if I don't smell actual cigs and get the same vomiting and headache. I go through bouts of smelling dirt (ask in fresh turned earth) for months too. Which at least isn't unpleasant and doesn't worry me about fire. The bad things is that a lot of food smells bad to me (as in past expiration). I've eaten things I could not smell or taste were bad and got sick a few times. So now if the date is past I throw it out regardless.

The smells usually do go away and cease bothering me. I had one doctor call these olfactory hallucinations. Hallucinations are a side effect of several PD drugs so some of this could be hallucinatory in nature.

The thing is I was diagnosed as not having PD very recently. As I taper sinemet I am regaining my sense of smell. I can smell coffee in starbucks or my house for the first time in years. I am getting less and less inaccurate smells as in everything smells of dirt or just weird and not like I know it does smell according to friends or just knowing cheddar cheese doesn't smell like burning plastic.

I'm not so sure the PD or the drugs don't do the number on our noses. At least it does seem to change so that you may not be driven nuts by a bad smell for more than a few months.