It does sound like he has a hearing loss. The reason he would jump when he is in your lap is because he can feel the vibrations of your voice and feel you move.
I have a hearing loss that was not diagnosed until I was three! My mom kept telling doctors I couldn't hear, but they refused to believe her. Fortunately, interventions have increased dramatically since the late 70's.
Hearing aids have also improved dramtically since I first started wearing them. The younger someone is when they get hearing aids the better! Then the feedback and background noise that can occur with them becomes normal and we adjust to that. If you have other questions, please ask. I will try to answer them. For now, look at your son when talking to him. That should help some. I can also give lots of advice about how to help him in school later if it does turn out that he has a hearing loss. Please keep us informed.