The snow seems to bring out musty damp smell from the house

[Mimile]

Our house is not usually damp - I have nevertheless put the dehumidifiers on. Barely a drop of water collected in >4 hours.
Since the beginning of the snow, the house has got a really strong musty, damp smells. I have tried to find out the source, to no avail.
Candles and sprays only disguise it.
We live in a 1930's terrace with "floating" stripped-back wooden floors. I know that when we did replace the central heating, the guys lifted the floorboards and we could see that the space underneath had quite a lot of rubble / building site crap.
Anyone knowing what is happening / what we could do? First time this is happening in 3 years.