Good morning, and my apologies for missing you last night. The multiple messages can get lost in the queue so I didn't see any of them pop up last night.
Unfortunately, the issues you are experiencing are symptomatic of an internal hardware defect, meaning a faulty amplifier circuit or main/control board, though there are many possible failure points. This issue could be a manufacturing defect, but is also often caused by a power event (shock/surge, prolonged over/under voltage condition, etc).
This could also be the result of age related wear and tear; as a 2013 model tv, that type of failure wouldn’t be surprising.
There is one step you can take here, both as a possible fix, as well as a diagnostic evaluation:
1) Unplug the power cord from the outlet
2) Wait at least 1 hour (60+ Minutes)
3) Press and hold the power button (on the set, not the remote) for 60 seconds
4) Keep holding power button while plugging back in, and for another 60 seconds after. When plugging back in, go directly to the wall outlet, bypassing any power strips or surge protectors.
If this reset process does not work, it would unfortunately confirm an internal hardware failure.
This is something that would require repairs to correct;
If you’re considering repair at a local shop, you’ll find a typical repair to be around $300 for diagnostics, parts, and labor to replace the main board.
A better alternative to repair, other than replacing the tv entirely, would be to connect up an external sound system instead, such as a soundbar: http://amzn.to/2bv1QrU
It will cost much less than repairs, and give you better quality sound in the end as well.
Depending how you’d like to proceed here, I can also help with finding parts, finding a repair shop, or recommending replacement options. Just let me know.
Best regards, ***** ***** for the news,