I have two CRDs, one sport and one limited. some how the limited is a bit smoother and more quite. However, on my sport the right mirror vibrates a bit at highway speeds and on my limited it is the same but on the left mirror
on both you can feel a bit of vibration at the steering wheel and at shot-off, but not anywhere else, those vibrations are not disruptive of functionality at all. What is the mileage on the liberty? both motor mounts on my limited failed at 69000 miles, and at 87000 on my sport causing all sorts of weird vibrations and noises. If you visually inspect the mounts you wont be able to see the difference between a good one and a bad one but if you take them off and shake them you will hear like if they had marbles inside (maraca effect 
)which means they went south. I think it is due to the fact that they are not only motor mounts but also insulators and they have hollow areas inside, but I am not really sure on that one. I would advice to replace both. they cost about 90 bucks on line and they are probably one and a half hours worth of work.
hope that helps any.
these are the part numbers for both mounts if you need them
52129374AC
52129011AD
