Rear suspension noise when going over bumps in road?

My 2002 Hyundai XG350L with 47,000 miles used to be a very soft riding
car. It has brand new Michelins installed 4 months ago. This new noise
just started two weeks ago. When going over a bump (most often a
raised bump like a pavement blowup) the rear suspension is very noisy
and hard riding. When the rear tires drop into a pothole or drop off
there is little noise. Struts are not leaking. Everything looks good
from an initial visual inspection. Car was 4-wheel aligned and the
alignment just rechecked. Tires are correct inflation all around.
I replaced the inner U-shaped rubber stabilizer bushings and it
initially moderated the noise but the ride was still harsh. I then
replaced both outer links last weekend. Now there is little or no
noise but it still rides like I have bricks for rear struts. With so
few miles could the struts be bad? Would they ride fine most of the
time and be ok when encountering dips in the road but be very harsh
for bumps? I am stumped and my full warranty just ended.

 

On some vehicles, the upper strut bushings are made of a material similar
to foam and they rot away. The new bushings are made of rubber.

 

Are these bushings shaped like a donut? At the very top of the strut?
There was material that was coming off of the top of the strut tower
on one side. Would these be the bushing A and bushing B denoted on the
exploded view drawing? Or the urethane spring pads.

 

I'm referring to "bushing A" and "bushing B." I'd say they're shaped more
like washers than doughnuts. One is tapered, and the other isn't.