This is just a speculation, but I think Mr. Ben Burtt may have been watching a bit of Bladerunner when developing some of his WALL-E voices.
There is a scene in Bladerunner when the genetic designer JF Sebastian enters his apartment with Pris, and calls out “Yoohoo, home again” to his toy friends. WALL-E’s “Yoohoo” sounds exactly like that of JF’s.
I did some google searching on this but did not find anything regarding the similarities. I was just wondering if anyone else had come across this.
I’ve never seen Bladerunner before, so I wouldn’t know. But “Yoohoo” is a pretty common thing to say, but I guess you mean they sound exactly the same. I’ll have to check that out.
Yes, I’m pretty confident the “Yoohoo” sound was lifted from Bladerunner and altered in pitch slightly. TBH it wouldn’t really surprise me as WALL-E has so many homages to iconic/cult Scifi films anyway.
If you haven’t done so already, I’d recommend watching 2001: A Space Odyssey, Silent Running and Bladerunner as they are beautifully made films with strong emotional themes.
I never really realized that what Wall-E was saying was “yoohoo”. It sounded more like a high-pitched, robotic whistle to me.
Now I’m interested to see Bladerunner, I’ll need to check it out.
I always laugh when he goes “yoohoo!” coz my grandma says that a lot. 
I just assumed it was a dialect thing but obviously not.
“DEFINE: Saying Yoohoo.”