You say 'for no reason'. Does this mean that these behaviors happen completely out of the blue - or appear that way? Most child behavior theories argue that no behavior is without a trigger / underlying cause, it's just sometimes very tricky figuring out what that trigger is. Once you know what's driving the behavior, you'll know how to address it.

There's 1001 things to consider - diet, sleep, hunger, thirst, sensory issues, language (both expressive and receptive) difficulties, vision, hearing, attention, feeling frustrated, unheard, overwhelmed, frightened... If you're not sure at all it can be really helpful to document behavior. Firstly, overall - just make broad notes about what he ate each day, when and how much he slept and what he did as well as noting the timing of behavioral 'incidents' within all of this. Secondly, document a few of the more typical incidents in detail - context, company, lead-up, specifics of the behavior and exactly what happened after. What he did, what others did... what were the consequences - both intended and incidental. This often helps to reveal a pattern. Of course... at the end of the day it could just be a combination of personality and age, 2 things you can do far less about! But even tough little characters have their needs and triggers and can be helped by understanding what sets them off.

If this all seems overwhelming, this is something that a behavioral psych would do. Might be worth a couple of sessions just to help you get to the bottom of it, get some strategies and allay your DH's concerns. If you do this, chances are, they'll also ask you to document behavior so it might be worth doing this anyway to save time, money and explanations during expensive consultations.

Feel free to PM if you want to chat about this further.