This bugs me:

Bug: Red bell peppers smell funny. But they haven't always done that.

To reproduce: Cut open a red bell pepper and smell. Wash it, fry it and smell again. The smell is still there.

Versions: most red bell peppers since about 2007 (don't quote me on the exact year)

Description:
95% of red bell peppers that I buy and cut open smell of the pungent smell that is in the room after you have grown 10L of E. coli. - My work required me to do that a lot in the past and I clearly remember that smell.
I have only rarely observed the smell in orange or yellow bell peppers. They usually just smell like bell peppers. Also, a few of the red ones smell ok.
- Lets not talk about the green ones. They are not ripe and nobody wants to eat them anyway. ;)
About 10-15 years ago I have noticed the change in smell of red bell peppers for the first time.

I have asked around amongst my microbiologist friends. Most of them have heard this question, recognise the smell, but have no answer either.

Different people have had different suggestions, e.g. that E. coli smell of indole and indole may be present in the ripe (red) bell pepper.

Why has the smell changed over time and what causes it?

Let's get to the bottom of it!