Hey there man. It could be a rock or it could be you have water/mud stuck between your pad and rotor. Is it coming time for you to replace your brake pads? Could just be a coincidence that you're hearing the squeal just after you washed it down. I spray mine down regularly after driving through a good rain and I don't hear any squealing. Just a thought.
i need help i went mudding the other day and when i left to go home everything seemed fine but after pressure washing my vehicle it started making a squealing sound coming from the front driver side tire. Could it just be a rock in between my heat shield and rotor?