I had a very similar issue occasionally the sounds would be really fuzzy (or more like electronically distorted). Panasonic TV via HDMI too.
If I changed channel or go back the menu it would usually clear. Sometimes even the menu sounds were distorted too. But then would go back to normal after going back to TV or selecting another channel or recording etc.
it was really random, I could never see a way to make it happen. this had been occurring on & off for many months but not regularly enough that I logged a call (and I couldn't make it happen anyway if an engineer had been called)
Some time later, my TiVo died (hard disk failed with blue lights on the front of the TiVo ), and it was replaced. since then I've not had this issue at all with the new box (same tv and set-up, just other issues now ;-) )
thanks for your reply, good to know I'm not the only one. As I have the Tivo to TV and TV to Home Cinema as well as Tivo audio to home cinema, I will remove the Toslink and just keep the audio via ARC from TV to HC. I must say I do like the Tivo remote which turns on my Tivo box, short blip, TV, long blip and the TV turns on the HC via the viera link as well as allowing me control the volume.
My TiVo has just started distorting audio for a second or so after changing channel, fast forward or rewinding, basically any action that required audio to be restarted. It clears after a second or so. I be ruled out my AV amp/optical signal by trying audio through the TV and the problem remains. I suppose my TiVo is on the way out.
Welcome to the Community, I'm really sorry to learn about the problems you're experiencing with your TiVo box at the moment.
I've been able to locate your account to run some tests on the set top box from our end, we're not seeing any problems detected at the moment although I'd like to monitor this for you. Could you reboot the box after reading this message and let me know when you've done that?