Ferg, I can speak for mine only, The Hard Top on my Blue Boy is very quite on the highway at about any speed. Much quieter than the Soft top. I even think it is cooler than the soft top! That might be due to the deflection of the heat rays and the top being well insulated and my soft top is not. I have even given the thought of possibly having a liner made for the soft top.
I have not given much thought to the noise level when the soft top in up until recently. When the soft top is folded away it serves as a bit of a buffer between the trunk and the passenger compartment. When it is up the buffer is no longer there, allowing a bit more noise to enter the front.
Which leads me to another idea I have worked on for some time. There is nothing between the trunk area and the passenger compartment except a thin piece of fabric. Nothing to protect the passenger (s) from a major injury or death should a fire from a fuel leak happen.
With that in mind, I fabricated a sheet metal barrier to seal between the two areas. It will serve two purposes, Fire protection and Noise suppression.
Back to the Hard Top! Mine fits very nicely. It does not squeak or rattle. It is easily removed and re-fitted by me utilizing several thick moving blankets laid across the back and slipped under the top.
You must be extremely careful when fitted, it can scuff the paint! I believe the different rubber pieces available are mainly the culprit. Some are soft but some are harder and possibly cause damage. Several Guys have stated the use of thin plastic underneath the mount area will help.
Bet you will get a lot of comments on this one