Quick Question

[on:]

Which episode was it where they did the whole opening song with mouth noises, and what was with that?

[Reply #1 on:]

4ACV06 - Bender Should Not Be Allowed on TV
4ACV17 - Spanish Fry

Billy West and John DiMaggio (Fry and Bender's voices) like to beatbox. So there you go.

[Reply #2 on:]

If I remember correctly, one of them was just the two voice actors beat-boxing, and the other has them beat-boxing over the normal theme.  I can't remember which one is which for sure, though I'll say that Bender Should Not Be Allowed on TV is the one with the normal theme in the background (and the character voices in the remix, not just the voice actors). 

As to why they did that, my guess is that they tried it out on the commentary for Put Your Head on My Shoulders (IIRC), and decided to give it a go on the actual show, why not? Hey, it was a neat change of pace, both times.

[Reply #3 on:]

Spanish Fry is where they did the whole thing beatboxing, BSNBAOTV is where they had them beatboxing over the theme.

  Hope I've helped!