This is a good question and it's something that a lot of people suffer from. I do believe that this one comes down to form. Elbow position makes a difference. If you have your elbows are out at 90 degrees, try bringing them down to 45 degrees. Then focusing on the chest when you contract the muscle during the rep while keeping the shoulders relaxed. Squeeze the pecs hard on each rep

There is a lot more I could say on this. What I am going to do is pass your question on to the guys at Advices Radio. They are recording episode 5 today and I told them I would pick a couple questions from the QA to send over for use on their show. They will be able talk about this a lot more in depth than I could write here. So check it out, episode 5 will be out this week (6-13-16) and I am sure they will have more to share. Advicesradio.com