How to fix high noise levels during on-set recording?

If you discover high noise levels on set, don't assume post-production can fix everything. First, identify if it's air conditioning, electrical hum, traffic noise, voices, or clothing friction. Turn off any equipment you can; if you can't, change the microphone position, add wind protection, or have the actors move away from reflective walls. For lavalier mics, check for clothing friction; for…