hi guys.
i have a 1999 v reg fiat marea weekend 1.6 16v 100 elx auto.
i have noticed a noise where best described as a large flat spot on a tyre and sounds like a thump of some description. it only kicks it at around 20 mph and gets faster until 30mph then its that fast it doesnt sound like thumping. some one said i have wavy discs so i replaced the disk and pads. the drive shafts seem fine and it doesnt sound like a bearings problem.im wondering if it could be the auto gearbox. the sound doesnt get louder when turning left or right but only kicks in when car is warm and only around 20mph.

anyone had this problem or know anything what it could be as im stumped and cannot figure it out.