3 Year Old Is Aggressive Towards Baby?

My 3yr would grab his brother's head and kiss it. This was very new and different for us because he took becoming a brother very hard and would stay as far away from baby for so long. The baby is 7 months old and crawling now, so my 3yr old seems to be more OK with him being around. Yesterday he kicked his brother from walking along the sofa and of course got in trouble. He later went over and kissed the baby on the top of his head, but also shook his head. The baby didn't care at all, but we told him to be nice. But today he did it again, but I noticed he grabbed his head so tight his hands were shaking and he had his mouth open pushing his teeth down on his head. Of course I ran over and stopped him, but it's like he does it when he is excited. He has done it a few times now and I don't know what to do. He has been hitting his toys and started on our shoulders. We tell him don't bite that hurts and he'll stop. I honestly don't know what to do anymore. We don't have any family who come over so they aren't around kids or grandparents. Any advice is good. He is also going to be going through speech once we approved so he doesn't talk very much.