Hey, do you remember Pete and Harry, the two rabbits who used to appear in commercials for Carnation Milk? Yeah, me neither. Did they even air in the Los Angeles area?
Well, here's a bunch of them. These are from the mid-sixties and they were animated by Playhouse Pictures, which was founded by Ade Woolery in 1952. Until it closed down in 2002, it produced a stream of mostly-wonderful cartoons, animated commercials, industrial films and movie titles in a wide array of styles. They did the titles for It's a Mad, Mad, Mad, Mad World, for example…and the first animated spots of Charlie Brown and Snoopy.
You can find out more about these Carnation commercials over at this website. There's a newspaper article there that says the voices were done by Al Hammer and Lennie Weinrib. I assume we're talking about Alvin Hammer, a character and bit player who was in a lot of movies and TV shows back then, though I don't know of him doing any other voicing for animation. I'm not familiar with his voice but I'm going to assume he's playing Harry in all of these.
Pete is pretty obviously Lennie Weinrib in the last of these commercials but not the others. I think there's at least two other guys doing that rabbit's voice in them and one of them sounds a lot like Pat Harrington to me. Others may disagree…