How long have you had the fistula? Any numbness or discoloration?
Steal syndrome is when the blood supply is rerouted (hence the name steal) away from where it used to go, and can cause this sometimes.
http://en.wikipedia.org/wiki/Vascular_access_steal_syndromeI just got my fistula last wednesday and today bought a cheapo $10 stethoscope at the local mom n pop pharmacy. I thought it might be junk and would wind up getting a Littmann online later but surprisingly it works quite well! I can hear the bruit just fine with it. Nice wooosh woosh sound. I recommend anyone with a fistula get a stethoscope if you haven't already.
CVS didn't have any stethoscopes. They had telescopes, children's toys, and even floor standing home theater speakers but no stethoscopes. Go figure.