I have a Gainward FX5900 U and experiencing no such problems with flickerung etc, or any noise issues.
I first had an MSI FX5900 U but that caused severe graphic corruption on my rig, returned to supplier who deemed it faulty and replaced with the Gainward. This card for me runs like a dream even OC at 490/940 no problems at all + it runs very cool even under full load.
Athlon XP 2500 @ 2230 (11 x 202)
Abit NF7-S V2.0 (Bios18/nForce2.45 Remix/Dets 45.23)
512Mb Corsair XMS 3200 (22.214.171.124)
80Gb Maxtor SATA-150 (8Mb) 7200rpm
Gainward GS FX5900 ULTRA 256Mb
TT Xaser II 6000+ Case + TT 420w Silent PSU
LG 52x Burner/Aopen 12x DVD ROM
SBLive 5,1 + DT 2200 Spks