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The hissing sound followed by failure to produce any sound at all, could be a sign of either
A. internal amplifier failure
B. reception failure of the Bluetooth connection.
I would say that (B) might be a bit more likely, since it now does not even produce a hiss. (Try turning its volume up to be sure of this.)
Also, try a reset of the sound bar. The fault might possibly be there, if you have no other wireless devices or Bluetooth devices working off of the sound bar. A reset of the sound bar would be as follows:
- while it is On, unplug it from the power, sharply and suddenly.
- leave it that way, unplugged from power and Off, for at least 1 hour.
- plug in again only after that interval, and try it out again, re-Sync-ing as necessary.
How old is the subwoofer? how old is the sound bar?