Well they shouldnt, and the only reason they do is for cheapness or because they didnt realise they have bumpy bits!
So, ones that look properly, fit right and avaible in: (can you sense the hard sell?)
GRP
GRP Flocked
Carbon Fibre
Come visit me at Bingley to have a look at em, and since not done GRP or Flocked before thats where you will find the prices (and posted on here after show)
These are sold and used in competition, they are a VERY tight fit, but would be better in a road car when bonded down to stop the rattleing.