I had a similar problem with the Nano Flash and my tape VariCam when I used the pre-record on the Nano, but it was only the Nano files that were affected and only if the pre-record was on. I sent CD the files and my Nano and they could not duplicate the issue. They sent me a brand new unit and it did the same thing. My only solution was to not use the pre-record.
Hopefully they can find a fix for you guys, it is a pain, and a lot of times not practical, to power things on the camera with separate power sources. Right now you can't use a wireless receiver on a C300 and power both from an A/B battery plate. At first it introduced a ground loop hum/buzz into the audio and after the last firmware update(not the one that came out this week), it turned into TC bleed.