Microphone not working when videoing

Got a phone in today where the microphone works when making calls, and voice memos etc, but when recording video all i get is a static sound, If i yell really loud or tap the back of the phone you can hear it vaguely but it leads me to believe there is more than one mic, one of which is faulty. I thought it might be a mic next to the rear camera connected to the lock flex, so i replaced that but the same issue. Would really appreciate any help.

Cheers