This happens on mine also. Very annoying. A bit of searching shows it is a common issue on these sound bars. Stay well away from these.
I think it is due to overzealous power saving in the sound bar that mutes the sound during quiet parts of a film etc. You'll find that if you switch to your TV speakers when this happens, the sound is normal.
BTW sorry for the necro bump. I realise this is an old post but Internet searching for a solution to this problem brought me here.
Has anyone received a satisfactory response from BT or JBL on this annoying fault? Thanks to those from the forum who gave attempted a solution. Unfortunately none works.
I have a Sony Bravia TV connected to the JBL Sound Bar received as a gift for upgrading my account.
Is it just a case that we accept this poor device because it was free?
I had exactly the same issue and phone JBL support today (01612223325) - found the phone number here. Very helpful - they checked my serial number, and sent me an appropriate firmware update. They said it's a known issue.
They include a PDF with instructions, and a .bin file which is the update itself. The only issue I had was that the first USB stick I tried to use (Sandisk cruzer) wasn't recognised by the soundbar. The second one worked fine (a generic cheapo stick).
I've played a few video clips and haven't had the issue yet... but I'll need to give it time to be sure.
I rang the number you supplied and like you eventually got an email with firmware and instructions. Have the serial number ready else it might be a frustrating call.
Any info regarding the existence of the upgrade or the upgrade itself cannot be found online, a phone call is the only way.
The new firmware is version 42.37. It loaded ok but please follow instructions using buttons on unit, not the remote control.
I checked the firmware version after upgrade and it seemed to have worked. Note that I left it upgrading for a couple of hours ( not the 14mins it says) and it still did not indicate the upgrade was complete.
It's been a day now and I have not had a reoccurence. I will update all if that changes