A warped disc can sometimes be felt through the brake lever aswell. As you ride along then apply the brake it can make the lever pulsate in and out depending on how badly warped it is and how long it's been like this. Sometimes it can be heard while simply pushing the bike along, each time the wheel turns the high spot can be heard rubbing against the pads at the same spot. If it's purely a shudder your feeling it could be the head stock bearings. Try applying the front brake while standing next to the bike and rock the bike back and forwards, if they're loose (or knackered) you should be able to feel the play. (if they are, try replacing them with taper roller bearings, far superior & less maintenance intensive) but dont over tighten them what ever you do.