It's normal for all new TV Speakers to sound like crap. Most people plan on using something (anything) else from day one. I mean how much high end fidelity are you getting out of your Cell Phone speaker? Expect similar service from modern TV Speakers.
I use a Cheapo set of Desktop Speakers with the woofer (40 bucks at Amazon) plugged into the headphone jack and that setup is 1000% better than the provided TV speakers.
You could return the unit in the hopes that the next one sounds a bit better, but my advice is that sound you're hearing is a just a reminder that you need some auxiliary audio equipment. When you acquire this equipment, if you discover the same sound, keep the audio equipment and return the TV. Whatever you get in replacement is going to need that audio equipment.