Thanks for the clarifying comment; I take a liberty in quote them:
How old is Bob? How much experience does he have (cf the rest of the team)? How does he perform in general?
He is older than the rest of the team, but has less experience than some (he was out of work for several years). He is not an especially high performer because he is in a collaborative role where he has to communicate with other departments and really struggles with that. His technical skills are good, otherwise he would have been fired under his previous manager. I haven't had a review with him yet, but he has consistently "needs improvement" reviews.
Sounds like a blossoming insecurity. I am not a psychologist, you also are likely not, so not much you can do to alter his behavior. Talk to HR; they are in the position to ask him to take counseling.
Meanwhile you do have some tools to your disposal. Change his role to more technical and less communicative. Or put him on a performance tracking program. It really depends on how do you see his future in the team.
That said, I really don't see why his mode of speaking annoys coworkers that much. They are professionals; they should see what he says, not how. There is no place for sensitivities in a professional environment. His excuses shall not impede disagreement. This is what you should convey to them.