Under the house
Musty smell indoors, worse in July and August
Humid outdoor air is getting into the crawl space and condensing. The smell travels up through gaps around pipes, ducts and the floor itself.
Floors that feel soft, bounce or dip
Joists or the beam under them have been damp long enough to weaken, or a support has settled. Someone needs to look at the wood before anything is covered up.
Insulation batts sagging or lying on the ground
Fiberglass soaks up moisture, gets heavy and falls. It tells you the air down there has been wet for months, not days.
Puddles on the soil after a storm
Roof water or surface water is getting in, usually at a low corner or under the access door. It has to be drained before a liner can work.
Sweating ducts and rusty metal straps
Cold ductwork in wet air drips all summer. Drying the air is the fix, and a dehumidifier does that only if the space is closed.
In a basement
White powder on block or concrete
Water moving through the wall leaves mineral salts on the surface as it dries. The powder is harmless. The moisture behind it is the thing to deal with.
A wet strip where the wall meets the floor
Ground water is rising under the slab and coming up at the joint. Sealers on the wall will not stop it.
Water from one crack or around one pipe
A single entry point can often be closed without draining the whole basement.
A sump pump that runs constantly, or sits silent in a storm
A stuck float, a failed check valve, a discharge pipe that sends water straight back, or a dead pump.
Outside
Downspouts that empty beside the foundation
A roof sheds a great deal of water in a Tennessee thunderstorm. If it lands at the wall, some of it ends up under the house.
A dip in the yard that is getting deeper
It may be a sinkhole forming. Do not fill it or run a drain to it before reading the county's rules.