I'm sorry to hear that you're having this issue.
Some sound modes will sound better than others, and since audio signals can differ, the result may vary as well.
That said, if you think there's a problem with the unit itself, you can have the unit serviced by calling 800-SAMSUNG if you aren't able to work something out with the retailer.
This soundbar continues to create a hissing, vibrating sound when the volume is above 20. The best way I can describe it is that it sounds like way too much treble. When in Cinema mode, it is unbearable. What can I do? The unit is 2 months old. I'm thinking about returning to the store.