I leave mine on 90% of the time. I actually haven't take mine off for over a year right now, and probably wont take it it off again until next April. It's a lot quieter, and I like the way it looks, plus it has better rear visibility and a defroster. I would say the noise level of the 986 hardtop is similar to a small sedan, there is still some road noise and you can hear the engine, but less so than with the soft top. With the soft top I normally have the volume of my Becker CDR220 at 18-20, with the hardtop I am normally around 8-10.
I did add a front and mid strut brace which I think helps with any creaking when going over uneven surfaces. I have a lot of hardtop info on my website under info>accessories.
