I know this sounds strange, but the volume of the freeview channels is lower than the BT internet channels. I have had the UHD box for a few months now and no settings have been changed.
If i connect my tv aerial directly to my tv the freeview volume is louder.
I have the volume on the box set to 100 and i control the main volume with my BT remote. Main volume usually stays on 10, but recently i have had to crack the volume up on the freeview channels and when i switch to some BT channels the volume is way to loud.
I dont have the UHD box but I do have the Youview + G4 box and also have the Youview volume set up to 100.
I find depending on what you are watching that some channels and programmes sound louder than others.
I have even got TV volume on my Samsung full HD smart TV in living room at volume 25 and if dads watching I have to put the volume up to 30 as hes in his mid 80s and has in the last few years started going partly deaf.
TV in my bedroom is also a Samsung and I also have a Youview box conected to that and again Youview volume is set at 100% but I get that TVs volume at 30. As some channels dont seem as loud as TV in living room. TV in living room is a 32inch and TV in bedroom is a 22inch. TV in bedroom is a late 2012 model and TV in living room is a mid 2013 model.
Netflix seems loud on TV in living room as well as TV in bedroom on most programmes and movies.