Bad cables are something that should always be checked first ... also, many people do not push the HDMI end into the jack all the way.
HDMI cable is different than an Ethernet cable ... HDMI is a slender narrow metal end, which carries audio and video , while the Ethernet cable has a smaller box type end, usually plastic with a lock tab on it, which locks in place and should be pressed first before trying to pull out of the jack. .... Ethernet cable carries the Internet/Network feed.
Many Ethernet cables go bad from people just yanking them out.
After a few months of intermittent attempts to rectify my audio problems (dropping audio for a second or two every few seconds) I found a fix for my system. I turned my audio output in the settings for my fire cube to stereo output and let my reciever up convert the audio signal to surround sound. I believe that the first issue was my cube outputting a 7.1 surround sound and my reciever was trying to reconvert the signal... essentially bottlenecking the signal. As soon as I changed the setting of output the sound became flawless. Hope this helps!