If by 'perm' smell you mean a peroxide or ammonia type stink then it could be the urine of cats or (shock horror) rats/mice that is causing the odour. Look for points of entry and droppings along the skirting at the bottom of the walls.
Another possibility might be a leak in an interior drainpipe - check any joints in pipes that run down through the basement.
Then there is the washing machines themselves. These will be fitted with filters that remove fibres from the water when the machines empty and go into the spin cycle. This prevents blocked pipe-work. Along with the fibres there will also be an accumulation of skin scales that could be rotting merrily away -and causing a stink - if the filters haven't been cleaned out on a regular basis.