I too would suspect the tires first. Pull both fronts off and inspect them carefully for any unusual wear. Look for bulges, dimples, flat spots, or odd tread wear. If you find bulges, big dimples, or flat spots get the tires replaced immediately. These are signs of de-laminating tires. Which will result in a blow out. Also look to see if you're missing a wheel weight.

If the tires check out you could also have warped rotors. Try pressing the brakes slightly and see if you feel any pulsing in the brake pedal. If not then they are probably okay. You'd probably have already noticed this. It tends to get worse the harder you brake, and is pretty noticeable.

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