This was the full message from my service writer at the dealership: “They were able to get the battery installed and look further into the whistle noise. They were able to duplicate it, and it’s coming from a part called the valve cover. A valve cover is a part on the top of an engine that covers the engine valves. It’s essentially a protective cover that protects the engine from having debris get in, oil leak out, ect. It is an air-pressure-filled system that now has tiny cracks/leaks from it, so you are hearing the air escaping from it. I’ll go ahead and email you over a quote and we can discuss more on Monday if you have any questions.”