hi, i have a weird problem with my car, in 4th gear at around 50mph, if i dont have my foot on either the gas or brake, the gearbox will vibrate a fair bit, but if i have gas or brake pedal depressed, then the gearbox lever doesnt shake. it doesnt happen in 3rd or 5th. its a '99 a3 1.8 t sport. anyone know what it could be? i think the tyres will need recalibrating at some point, but that wouldnt be related to the gearbox lever problem, would it??