looked out to see this

bit of a rusty tinge.. so feared the worst.. coolant / failed rad..:bang:
coolant hadn't looked too scabby..but the car has been sat for @4 weeks.
Anyway coolant level is fine..,
I'm wondering if it's been filtering rainwater through the bumper / undertray support structure.. colouring as it goes..??
anybody had this..??
hoping to get it back on the road 1st April.. so don't want to have the front end off in the week before the FF meets/ shows:bang:
Charlie

bit of a rusty tinge.. so feared the worst.. coolant / failed rad..:bang:
coolant hadn't looked too scabby..but the car has been sat for @4 weeks.
Anyway coolant level is fine..,
I'm wondering if it's been filtering rainwater through the bumper / undertray support structure.. colouring as it goes..??
anybody had this..??
hoping to get it back on the road 1st April.. so don't want to have the front end off in the week before the FF meets/ shows:bang:
Charlie