More Vibration Woes

[vex]

Simple questions I need an answer to. I have a non-violent vibration that is concerning me. While accelerating there's really no vibration until I get around 50mph or so. Once there, if I cruise at 50 the vibration is usually constant and feels like it's coming from the rear. The rear end also feels a little vague, but I've had the bushings replaced recently (within a year). When engine braking I get a stronger vibration that is not constant. Usually has a strange vibration pattern to it on top of the normal vibration.

Would getting an alignment help this situation. The car doesn't really feel like it's pulling any direction, but maybe the toe or camber has come out of spec on the rear? I believe this is a development from the previous vibration issue I had which turned out to be a siezed drive shaft. I've since replaced it and this is what's left.