The HDR Fox T2 has never suffered sound drop outs due to the BBC HD encoders. My parents’ Sony TV used to have the issue before I upgraded its firmware, but the HDR Fox T2 never exhibited the problem whatching the same programmes.
Note the drop outs only affected BBC HD because only the encoder for BBC HD switches between 1080i50 and 1080p25 dynamically. BBC1 HD does not do this and has never had the sound drop outs, and you report the problem on BBC1 HD. So whatever it is it is unrelated to the i/p switching issue that affected Sony TVs. I suggest you check your cables and your amp.