Polk sound bar 3000 not playing sound when tv comes on

we love our Polk 3000 soundbar. Usually when we turn on the tv, the sound comes right out of the soundbar as expected. Lately though, we power on the tv, the soundbar comes on and there is no sound. For a while we just turned the power off and on from the front of the soundbar and that worked. Now though we have to turn the power off and on with the switch in back of the bar ... And it comes on very loud. any Idea why the sound isn't coming out as normal when we turn the tv on?

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