Note: Kyle is showing REAR bearings in his picture. TOTALLY different animal here, IF, your talking front bearings. AND, thats what I get from this posting. "nasty shake"............is my key.
Many things can cause this "situation".
IF.....you are asking this question in the way that you are, than I must assume, that you don't have much mechanical/car experience. Correct?
Just know for one thing. Just because you had your wheels balanced, doesn't MEAN, it was done corrrectly. Question everything! Start with the most "cheapest", and go from there............IF..........thats the best you can do. DON'T "assume" anything.
Clark's garage is another possible source of info. Taking it down to a "reliable/familiar with 944's mechanic" might be a good idea. Let them diagnose it, than YOU repair it.