My GH4, pre-ordered in March, had the dreaded buzz: a sound like a motorbike or motorboat idling constantly, very slightly audible in very quiet passages. While it was “mostly harmless”, on occasion it would intrude, and I’d wind up having to duck the level in post any time things grew quiet. Certainly it was worse than the sound I recorded using the GH3.

Read the full article: The GH4 Audio Buzz Fix - DV Info Net (http://www.dvinfo.net/article/acquisition/micro-43/the-gh4-audio-buzz-fix.html)