Most likely caused by either inadequate rinsing shampoo off after washing the car. Most tap water contains lots of added chemicals, so even clean water can do this if left to dry. Always best to dry these strip with a micro-fibre cloth after washing.
I've found that using some liquid resin polish (eg Autoglym) clears it up and adds some protection. As always, try a small area first.
Best thing to get that off with @peterh (in my opinion) is Gtechniq M1 All metal polish. Not cheap, but I've had excellent results with it, all you need is a small dab on something like a makeup removal pad (I'm sure the wife must have a spare LOL) and that should clean it up and give it some protection