^ I would second that, a few if not all of the struts are probably blown from drop springs and age.
Test it by standing over the wheel well of each wheel and pushing down on the car. There should be little rebound, if its just wobbling around they're more than likely the issue.
That hollow clunk sound is a very clear obvious sound though and I just had this issue a month ago.
check your end links and sway bar bushings.. this was my problem.
I hear a clunk from my car on every dip or bump. The clunk was still there after changing the endlinks so i decided to replace the sway bar bushing. I got moogs and they gave me the wrong one. apparently the lx has a thicker sway bar than the ex and dx. So i popped my old ones in, drove to the place and noticed the clunking noise was gone. I just took em out, cleaned the bushing and where it sat
Hmmm you sure...
99 LX front sway bar bushing is part# 51306-S84-A01 no matter if LX/LX+ABS/Ex
DX is different 51306-S84-A32
V6 is different 51306-S87-A01