has anyone noticed this in the e28 model. it mainly happens when you are breaking or slowing down. common on offramps, but even evident in the city. has anyone found a solution? what is causing this to happen?

Very common. Thrust arm bushing (aka. upper control arm). Replace the whole arm and get a new ball joint too.

how much is all of this?

A little over $100 for the pair. I'm assuming you'd do the labor.