2001 Kia Sportage driveshaft problems

I have this sportage that my oldest son drove the wheels off. Now i am stuck repairing it and making it a daily driver to and from work.
I noticed this evening coming home from work, that a vibration and noise was coming from under the car.
I got home and crawled under the car to "look around"
I noticed the driveshaft is a two piece unit with a bearing or something in the middle. After messing around with it for a few minutes, i noticed ( or at least feel ) that this to really loose fitting.
I did notice on the way home, that once i got up to speed the vibration would settle down, and the noise went away, which i why i am assuming this could be the issue. As the driveshaft increases in speed, the unit "might" center itself causing less vibration and noise.
Does anyone know what this unit might be called, and if in fact it should be a tighter fit that it seems to have ??
Hope someone out in the net world might know something that could help me...

Is this a 2wheel drive? the 4x4 has one piece shaft to the rear....or..well, I mean it is not supported by an extra bearing in the middle.....is this rather the telescopic part of the shaft you are talking about ? It might be worn out. It has a greaser in or near the middle .
http://www.avigex.ca/kia/drivingshaft.gif

My problem sounded the same and investigation revealed that it was a worn out rubber mount for the most aft exhaust pipe mount (after the muffler)...it would rattle horribly at idle...there is a shoulder bolt that keeps one from simply tightening the bolt, so I added some fat washers until I can order the replacement rubber from the factory as am not able to find these parts locally.

...exhaust pipe mount (after the muffler)...it would rattle horribly at idle....
Indeed all exhaust pipe shields will also pay vast amounts of noise, rattle, you name it. That is why I suggest posting "sounds" just as we do with pictures; most digital cameras can capture sound clips and posting that would possibly help identifying and discriminate sound, rattle, humming, rumble, chatter, vibration....:rolleyes:
Check this one out: www.avigex.ca/kia/Snd_2403.wav . Just a test, but another forum member replied I had an automatic(which is correct)....because the manual does not have the same starter gearing and the noise is different...which I did not know.