Vacuum Cleaners Discussions

Sorry to keep asking so many Dyson questions.  This topics of this forum seem to be mostly about big box brands anyway.  I don't have to ask questions about my Kirbys and Hoover Convertibles... I can understand them! 

Anyway, I used my Dyson DC14 (should have gotten a 17 or at least an 07 instead, this must be the worst model of all) at a friends house.  He has a Bissell Clearview vacuum... a cheap Wal-mart special.  When I went to his place, my Dyson barely got anything up.  His Bissell got up a lot more dirt afterwards that my Dyson was not able to pull up.  Probably due to the weird brush roll.  The suction and air flow on my machine are fine, so I'm starting to think it's the belt that is the problem.  When I push the machine forward fast while its running, I hear a weird rattling sound. 

My question is, even though the belt is SUPPOSED to last a life time and the user is not SUPPOSED to be able to change their own belt w/o taking it to a Dyson authorized service center, how can I do it myself?  Do I have to buy the whole clutch assembly, or can I just get the belts?  I'm not worried about voiding the warranty, since I bought the machine used. 

Any advice?

TIA  :o)