What might cause sense of taste and smell to (very selectively) change?

Factual Questions
1

A few weeks ago I was drinking a Diet Pepsi from a can (one of the last of a twelve-pack I’d drunk the rest of over previous days) and I noticed it tasted kind of odd–it had a weird musty aftertaste. I wondered if something was wrong with it, so I chucked it and tried another. Same taste. I figured it was just something weird (but nonthreatening) about the cans in that 12-pack.

Got another 12-pack. Same problem. Especially at the beginning of the can, it has a strange aftertaste…“musty” is the only word I can use to describe it. I noticed this later on in fountain DP as well. Diet Coke tastes the same as it always did.

I’d write this off to a slight change in DP’s recipe, but then I started realizing that I was getting the same sort of thing (as an aftersmell this time) from my bath products–liquid soap, and Aussie shampoo. Then a few days after that I noticed the smell coming really strongly from the spouse’s can of Red Bull (I’ve never liked the smell of that stuff anyway–as a friend quipped, it smells like “SweeTarts and ass”–but this was overpoweringly unpleasant, with the same musty overtones as before.)

Every other food I normally eat or beverage I normally drink smells and tastes fine–no change.

Can anybody suggest what might be happening? Is there an ingredient that’s common to Red Bull, Diet Pepsi, shower gel, and shampoo? Is it a case of my sense of taste/smell changing as I get older (I just turned 40 last year)? Have I got some horrible medical condition that manifests itself by subtly altering the smells/tastes of a limited number of items? Are space aliens experimenting on me?

Any help/suggestions appreciated. (BTW, I don’t smoke or do anything else that would normally be expected to mess up taste or smell.)

2

I get that “musty” smell/aftertaste on certain things when I’m a few days away from a full-blown sinus infection. Hopefully it doesn’t work the same way for you!

It lets me know when to stock up on 12-hour Sudafed and Puffs Plus, though…

3

Might be you’re simply noticing it more, that the smell was already incorporated into the different products, but now you find it because you’re looking for it… I grew up with parents who smoke. It took me until my junior year of college to be able to notice when classmates had been out smoking. And they thought I was just indifferent.

4

My sense of smell changed following surgery. Now I hate the smell of most things cooking. So much for taking a big whiff of a sausage sizzle when I walk past… makes me gag now. Sad, sad.