They're most likely using clip on weights on the svt wheel, cleaning the wheel unless its covered in mud won't really do anything.
Could be the tires, or they may not be balancing them correctly.
98.5 SVT
91 Escort GT (almost sold)
96 ATX Zetec (i brake to watch you swerve)
FS: SVT rear sway bar
WTB: Very cheap beater
CEG Dragon Run - October 13-15