Im in the man cave (cellar) most nights and have half the family here. Last night I could hear someone whistling underneath said bedroom which I thought was odd, so when I saw my mother I asked if she was trying to wake the whole house up whistling? Wasnt her.. Everyone else in bed asleep and this deffo came from the kitchen where she was. But she never whistles..
PS : FWIW I’ve found luminescent green/yellowish fungi (or rather mycelium growth) spread out over quite an area whilst out on night rides before, this was in one section of the galloway hills known as “the silver flow” which is a rather scary peat bog area in the absolute middle of nowhere – it looked like a humoungus spiders web trailed across the ground which (at the time) scared the shite out of me as i had absolutely no rational explanation as to why/what was happening.
No, I don’t think anyone really knows what it is. Try peeling away what’s covering it. Unless someone has buried a radiation source in your wall (seems unlikely), its probably harmless. If you can’t see it in daylight with a torch and you’re really scared then I suggest trying to find an organisation with a radiation detector. Local University?