Ever since the car was new it has made a loud "boing" noise when going over a high spot. I think it happens when the front left wheel hits the bump. It was intermittent. Noise seems to come from the left front. I brought it to the dealer 4 times to find the cause (the car never cooperated during test drives with a mechanic). Now, after it makes the horrible sound, the ABS and Tracs Off lights come on. Codes have come up indicating the ABS control module. I haven't found information on this website about this kind of noise. I'm worried that whatever is causing the noise has also caused the control module to fail. Service manager at my dealer says the noise is the ABS pump building up pressure. Noise is much more prevalent now that control module has failed. Noise now occurs without hitting bumps. By the way, car has 51,500 miles and is 3 months out of warranty. Just my luck! Any insight into this frustrating problem is appreciated.

How do you know what codes you have? Once the ABS/Tracs lights are on (staying on), the system is off so I can't see how it could then be causing ANY noise. On a '98 X70, the cause of the ABS/Tracs light staying on is (almost) always the control unit.
The "normal" ABS noise heard everytime the car first reaches 18 mph after starting the car from a stop is its self-test and that might be what you're describing? It's a mechanical/metallic type noise and I believe it's described in your owners manual too. That noise has nothing to do with going over bumps nor would you hear it if the ABS/Tracs lights are staying on (system is off).

The typical noise heard going over bumps or at slow speeds turning side to side is usually caused by worn sway bar links, a VERY common problem in newer cars like yours but it's easy to duplicate and any Volvo tech anywhere has seen and replaced many a bad one by now.