@Locksley You can usually smell it, especially after you come home and the musty smell is there. As @June1952 said, there’s probably damp if the home is dark and if the windows are not opened regularly. You can buy the damp absorbers as a cheap option. I buy the ones from Bunnings or Rejection shop, they’re $2.50 each and they absorb quite a bit, especially from wardrobes. After I discovered I had it at my old place (whole mattress got mouldy) I bought a dehumidifier that was about $400. On humid days, it pulls 5 litres of water from the air in about 3-4 hours. That’s how bad it can get.
Anyway, start with the small ones, and look out for the musty smell 👌🏻