Most issues with audio seem to be with the cables. I would take a look at those first. If they are in properly, take a look at the audio settings on the cable box. Make sure they are turned up all the way.
Check this link below. It should be able to better explain what to try:
Hope this helps!
Sling Media Moderation Team
The reply about the audio settings was a helpful clue. It turns out that with my M1 and Comcast (Motorola manufactured cable box), it is necessary to go into audio settings and make sure you are on 'stereo,' rather than Matrix, and then hit the optimize button. That got the audio going for me. Hope that will help someone else!
Thanks for your post. I have a Motorola DVR. When I first hooked up the M1, I wasn't getting any audio. It was a bit frustrating when you have beautiful video but no sound. I was stumped at first but thanks to your post here, I went into the DVR master setup. Like you said, the audio need to be set to stereo...it worked. Thanks again to your post. Extremely helpful!