1999 Dodge Intrepid 1999 Dodge Intrepid ( brake vibration )

Sometimes, ( but not all the time ), when I step on
the brakes, there will be a vibration. Although this
car has an ABS system, this IS NOT an ABS vibration' As a matter of fact, the ABS light has been on for
almost 4 years. The mechanic I took it too told me about the ABS module might be bad and would cost close to $400.00 for new one. And then he said I
really don't have to worry about it because the car
still has the regular conventional brake system. Actually, the car brakes fine - it is just very annoying
when it happens. I'm thinking I may have an
alignment or ball joint or suspension problem. Any ideas from anyone? Thank you.