Poor audio capture is rarely the microphone itself. Noise usually enters through the power and ground arrangement.

• Shared supply ripple: when the microphone shares a switching supply with the camera, ripple couples into the audio as a continuous hum.
• Ground loop: separate earth connections for microphone and recorder create a potential difference, especially when the shield is earthed at both ends. Earth the shield at one end only.
• Gain too high: winding the gain up amplifies the noise floor as well. Keep the front end low to mid and compensate downstream.
• Cabling and routing: unshielded cable, or audio runs bundled with power cable in the same trunking.
• Ungrounded housing: a floating metal housing picks up ambient electromagnetic interference.

Work in this order: give the microphone its own filtered supply, switch to shielded cable earthed at one end, then fine-tune gain.