It happened hundreds of times for me, not only here in Brazil or with Portuguese audio, so I don’t think this is a region related issue. Sometimes when I am watching a commercial a dial sound comes up (sounding like 5641 on a dial pad, I think). I recorded a video today of the issue: - YouTube. Is there a name for that? A reason?
I have heard this too.
Have a look here:
http://en.wikipedia.org/wiki/In-band_signaling
Scroll down to “Non Telephone”
wow, that actually makes a lot of sense. I never heard that sound outside television. Thank you, longPath!