What does it mean when I hear something pop off and spray coolant while driving

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. A pressure test of the cooling system will determine where a coolant leak has occurred. I suppose it's possible that the coolant boiled over from a reservoir cap or from the recovery bottle. If this happened I would expect that you would see evidence of coolant in that area. "Engine knocked" is concerning; was it overheating? Hands on testing of the cooling system is definitely in order. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.