Smell from my plants???

Hi my plants stink as any others do. Always worse toward the end of course but ive noticed that it becomes really strong at different times of the day but then other times it doesnt smell at all. I have a carbon filter and an extractor with duct leading out of my basement. I stood outside to sniff up. Some times it stinks other times nothing.
At first i thought it was something to do with heat coming from the lights but it happens randomly even when the lights are off.
Does anyone know anything about this?
Thank you

maybe the coal filter is old and needs a replacement ?!