Many where annoyed over the screaming droids in Revenge of the Sith. It was kind of silly and detracted from the awesome action that was going on in the movie.

I think however there's a perfectly logical explanation to it all.

The war has been going on for three years now and too win a war you have to be two steps or more in front of your enemy when it comes to innovations. The Republic had started personalizing the commanders so that they would think out of the box. Apparently this was a success so that Separatists thought that action needed to be taken.

Naturally, they would place a similar order, but here's the twist. They order every droid to have a personality. Methinks the Separatists weren't more specific at this point and those receiving the order must've taken some liberties when it came to the interpretation of the order

"Personality, personality. Let's see. What if...what if we gave them some attribute...like, oh, I dunno....humour! Yeah, we'll have funny droids! No? What do you mean "doesn't really work in battle"? Oh well, how about fear then? Maybe fear of screwdrivers? Wait, that's stupid. Fear of flight? Nonono, not efficient. We can't have pilot droids being scared of flying...I know! Fear of death! They'll defend their lives with everything! And we can but in this cool thing where they scream when being "killed". That might put Clones and Jedis off of killing them"

So there, I believe the droids screams because the manufacturers made a bad job of a bad order. The droids were supposed to put the Republic off from killing them, but alas, it did not work and the manufacturers got a heavy pay off for these "upgraded droids" and made a run for it

I can picture the scene right in front of me right now with Nute Gunray standing with Rune Haako

"Rune? How much did we pay for these "upgraded" droids"? Wait, on second thought, don't tell me...get me an aspa-aarin instead"