A person doesn't buy a convertible because they want a quiet car with the top up!

Seriously, with the top up my ride has no rattles unless you go hammering over a set of railway tracks. Also, anytime when the only thing separating your ears from the highway and the wind is a layer cloth (canvas), there's going to be more ambient noise. That's normal.
But to me, I didn't buy my vert to have the top up. It's always down when I drive. Only exceptions are if it's way to cold or raining. Then again, my car is only driven on "sunny Sundays".
I suppose when compared to other verts that might have a folding hardtop or an insulated and/or lined soft top, the '89 Camaro top would be a little louder, but again why buy a vert if the ambient noise with the top up is a concern?
I love my vert!