If it's new, pack and swap for another until it works. No company today sends techs out at this price part. Upsetting but true.
I have an LG SJ7 soundbar. I get a random humming through them. It lasts about 40 seconds and then stops. It will go for hours without doing it and then all of a sudden they just start humming. The first Soundbar I had did the same thing along with a loud electronic click once in awhile. Also the speakers would lose volume and then come back. I was sent a new pair and have the same issue with the humming but not the other problems. LG is no help trying to figure this out.