steering wanders on uneven pavement

Help!
Im a U.S. Citizen living in Japan.
I recently bought a 92' civic SIRII. JDM hatch with original B16a and Traction Control System.

I recently had the car aligned by a respectable tire shop on a computer aided machine.

The car drives straight as an arrow until I drive over bumpy or uneven pavement. Under these conditions the car pulls to either the left or right--it depends. Its slight but enough to cause concern.
The mechanic said it did the same thing when he test drove it, but he's not sure what the problem is. He does know that it was seriously out of alignment before I brought it to him. He also checked the air pressure. The tires are fair with maybe 70% tread.

Does anyone have any experience with this problem? I realize the car is 10 years old, but I have faith that it must be a worn out part(s) that could be replaced resolving the problem.

i have the same problem. i thought it was because of my worn uneven tires(cause i lowered it before, and fucked up the inner side of the tires, and now i am back to stock height).....are your tires new? this didn't happen to me when i have my stock wheels and tires.

btw, i have a 95 civic

thanks for the reply.
my tires aren't new but they aren't that bad. The car sits lower than my 92 VTI which has 14" wheels. It may have been dropped.

Does dropping your car ruin the rack and pinion steering assembly?

well, i dunno, i've driven lowerd cars and nothing like this happened before....:(

It happens with larger wheels and tires and/or stickier tires. Is that the setup you are running?

The car is bone stock. original wheels with Yokohama 195/55/15 (this is original equipment for the SIRII In Japan)

Someone told me it may be the wheel bearings. The car makes an unjulating noise that matches the speed of the car. i.e. the faster you drive, the faster the frequency of the noise.

:bloated: