Seen the picture and if I understand the problem, your getting some vibrating or touching noise on the backside of the acrylic and the front side of the roll bar tube.

Try getting some felt pads with self adhesive backing that can stick in the area between the two points. These felt pads are normally used for putting on legs of furniture and come in different sizes. I would think that this would fill any gap that is there and dampen the vibration you are getting. Give it a try; the cost is minimal.