Need to acertain whether the noise is from the audio circult or from external source.
- audio circuit > microphone inherited noise, impedance mismatch, wrong type of mic cable used, bad contacts between the connectors (oxydation), grounding loop mismatch, recorder's electronic inherited noise, 'dirty' AC current, bad phantom power, mismatch gain structure, etc
- external source > wind noise, vibration near the mic or from the mic cable (eg. floor, someone tapping/stepping on the mic cable), aircon duct vibration, recorder's mechnical noise (cooling fan, motor noise), recording setup placed too close to high power equipment, etc
Is it hiss, hum or rumble?
Hiss > most likely is it electronic inherited noise somewhere in the audio chain
Hum > most likely ground loop problem, impedance mismatch or dirty AC power supply
Rumble > most likely caused by strong moving air nearby the mic, or human breathing into the mic
Try to narrow down and solve.
Good luck.