Trailer is for a '99 MariStar, I'm sure the springs have sagged some. Yes, the trailer is level when hooked to my truck. I'm not really worried about damage to the prop or trailer, just want to get rid of the noise.
On the last boat I used to used a drop hitch to get out of the driveway without rubbing then change out in the street. Then I went to Tap plastics and put a strip of nylon under the prop guard to stop the scraping noise and damage to the driveway. The new boat trailer has casters so I don't have to worry about it. The nylon strip worked well though.
Try lowering your hitch on the truck first. That will improve the angle of your boat/trailer and make the back of the boat rise slightly. They make hitches that extend the ball lower. Should help.
Here is another idea: The angle you are leaving your driveway will help also. Turn your wheel a ton when you exit and don't hit the bottom of your driveway head-on. The angle alone will improve the exit and help make the rear of your trailer rise slightly. Try that and see if it works.
I have the same problem on my driveway. I just have my son throw down a couple 2x12's about 6' long under the tires and wheels just at the point where the prop guard will drag. The lumber raises the trailer just enough to avoid dragging the prop guard. A bit of a pain but it works for us. I
I had the same problem, but I needed more than 2" additional clearance. I ended converting my axle from undersprung to oversprung. If you look at your axle, it is most likely underspung meaning that there is no way to insert a block without converting to oversprung first. I purchased a conversion kit for $40, and it took me a couple of hours (would have been much faster with a helper). Most of the ramps I frequent are pretty steep so the extra height hasn't been an issue.
I had the same issue at our summer house. I would always drag the back end even with the casters at the bottom of the driveway and boat launch as it was a multi angled ramp. Last year one of the leafs completely snapped at the ramp so when I had it fixed I had the guy releaf them all which raised my trailer about 2-3" which made a huge difference and I don't drag at all anymore.