On unfinished basement foundation wall any sign of moisture/water check for cracks, if any open cracks seal/inject. Check grading if it is sloped away from home. If not improve your grading to prevent water pooling at foundation walls.
Also very important tracking humidity level between 30%-50%. Humidity meter can be buy from hardware store $20-$50. In summer if humidity level over 50% using A/C and de humidifire recommended to control high humidity level. High humidity level means high moisture in the air and potential of mold.
I seen many cold rooms with sign of moisture and mold. Many home owners block/seal ventilation at cold room and cause of high moisture on walls and ceiling.
Attic is most hidden place in your home. Attic is inspected by home inspector when buyin or selling home. Most common reasons mold growth at attic such as soffits covered with insulation,lack of ventilation,roof leak,lack of baffels and bath exhaust vent pipes discharged at attic. Mold remediation at attic may cost thousands of dollars.
Conclustion: If you observed any plumbing leaks,water penetration,roof leak,defective gutters/downspouts get them fixed as soon as possible to prevent mold. If you only suspect of mold call professional mold inspector to help you out.