Sometimes, we can be our own worst enemies.
The plating on the Bonneville's grab bar was really looking...sad, and instead of having mine redone (I still may), I picked up a really nice looking one on eBay, pulled my glove box, and swapped. Wouldn't you know it? I probably didn't get one nut tightened down quite far enough, as now, going over a rough patch of road (or a not-so-rough patch), the dang thing rattles... Grrrr... I think the rattle is coming from where the bar meets the dash.
The rest of the car is pretty rattle-free, even the top frame. One little buzz which has always been present (always=as long as I recall when driving myself, so since the car was 13 years old or so) is the speedo head when going over bumps. It doesn't bother me, though.
Good luck swatting your rattles. These things take patience and time.