It may be any one or a combination of some of the following. You've lost a balance weight on a front wheel, warped/damaged tyre, underinflated tyre, overinflated tyre, damaged wheel after hitting a kerb etc, warped brake discs, worn brake pads (excessive wear on one side is a possible),One front brake caliper isn't working (look for hydraulic fluid leak on the caliper mounted on the brake disc, worn suspension bushes or other components, worn steering rack. The wheels and tyres can be easily inspected by yourself. If you have lost a balance weight, there may be a clean spot on one of the front wheels where it was. Look for odd shapes and twists in tyres (front and back). If there are any unusual clunks or noises when braking suspect worn components. Any metallic sound may indicate excessive brake pad wear or even a stone etc stuck in the brake pad material. Finally check the upper steering column behind the steering wheel, is there excessive movement. Is it an adjustable steering column, if so check that it's locked in place properly. I've probably missed something but there's a few clues to the possible cause(s). Let us know if yopu cure it and what it was, just interested.