hey all i got 99 1.8t
when i drive abougt 140km or faster i start hearing a sound that sounds like plastic or something flaping there is alsow a vibrating ocuring under the floor.

its hard to explain but if any one has any ideas or sugestions ide appreaceat it thanx

when i turn left i hear my right drive shaft as well some times but i dont think that would have much to do with the noise im hearing.

 

Perhaps its your plastic belly pan that's flapping at high speeds. Maybe you have a screw missing or something and a corner of it is flapping or something.