haraldo23 said:

He's a robot. He's not supposed to sound different every time he tries to express his feelings. If anything - there should be the same sound when he's happy, the same sound when he's sad and so on.

Although, when you imagine all the little problems this movie had - you realize that R2's sound effects are the least important.

I'm NOT suggesting something needs done about this...its just an observation.

If you watch ROJ & the prequels you will hear the sounds of Artoo from ANH, and they are used as you say when showing his particular emotion at the time........but they are surrounded by newly composed expressions....an expanded library of sounds. ESB re-uses ANH and no expanded sounds. I remember when I saw the first clip of ROJ on TV....the part where Artoo & Threepio are at the gate of Jabba's Palace and hearing Artoo saying a new phrase......it really stood out.....6 years of hearing Artoo saying a limited amount!!

It's not a problem, just a suggestion.