Atem1 sound distortion

Hi,
We tried for the first time to use the audio from the atem1. The setup is as following: 2 sdi cams without sound, two mac mini with hdmi and sound. This is a live conference with powerpoints, videos and live feed.
Yesterday, at the rehearsal, halfway the show, sound from the macmini started to get distorted. After a few moments we got to the conclusion that there was problem with atem1, as we hooked up the mac mini directly to the sound desk and the problems were gone...
It was the second time we were playing the vids. At the first rehearsal there were no problems at all.
We are using firmware 4.0.
Any ideas. If this would have happened in a live situation this would have been very problematic!

Regards,

Gilles,

Blackmagic gear needs balanced audio connections. No shortcuts between the - and ground, or these things will happen.

Yes, I know. And this is what we were using. Output of the Atem to the Yamaha LS9 with balanced cables. We even shared the same power supply.
And in the beginning everything was ok. After some hours sound started to be unreliable.
Will setup the Atem again when back at the warehouse. I need to check if this happens again...
Will keep you posted.