Hi Ace. You can take a rubber mallet or hammer and "ta, tap tap" around the back of the transom. It should be "tap tap tap". If it goes "tap tap thud", then that sucks. Thuds are bad. taps are good. lol
Also, trim your motor up all the way without a support under it. Then push down (bounce) on the prop and lift up and down and see if you have any deflection on your transom. It should be rock solid. If you see movement, then you know what it's gonna take to fix her. You don't have to pop the whole top - can do just a back-half-cut if needed. I can give you all the info you ever wished to know. lol
Holler if you need anything. Rob 832-405-2980