My Mi 3 makes a weird noise near the earpiece around the area where the proximity sensor is located. It sounds like EMI or as if there are moving parts inside the phone. The sound is audible even when the screen is off and no calls are active. The occurance of the sound is random. But it will always make noise while the phone is booting. Sometimes it will last for a whole day. My phone is only 10 days old and not even dropped it once. Tried factory reset/ flashing a different rom, etc. It makes sound even in the recovery menu so I don't think its a software issue. Does anyone have this same problem ? Just try placing your ear near proximity sensor. I discovered it recently. Got a replacement but the replacement unit has the same problem !