Engineer on the way soon!
As there seems to be limited interest here in support of this issue (maybe cos I'm in the UK!) I've opted to call Samsung direct.
Didn't take long and helpful so far I'm pleased to say.
After describing the problem they are getting a repair centre to call me back to arrange a visit by an engineer to fix the problem.
I was told there have been a number of these issues so I hope they will actually turn up with a fix and not just listen to it etc..
Not sure if this is the right approach, but as I didn't purchase it and I've found a number of posts relating to Samsung vibrating speakers going back years maybe this is the best way to sort it out as everything else about the TV is fine.
Personally I think its the TV outer case around the speakers vibrating, but lets see what the engineer says..