So in April we ripped up our carpet in the hallway and stairs, stripped lots of old paint and painted it white. Since then we've noticed a meaty/musty/mushroomy smell that's worse when it rains.
I've cleaned the cupboard out and found nothing (bar a moth infestation that cleared when I binned the nasty old carpet fom there), and we've looked under floorboards and seen nothing untoward. Other than the smell there's no sign of rot or mildew.
A plumber fixed a slow leak in the top bathroom 5 weeks ago, but he didn't think this was a severe leak. Our dehumidifer put the humidity at 60%
Not really sure what to do beyond ripping the stairs up? It's not a strong smell and it's only after heavy rain. It seems to be improving since we cleared the cupboard up.