I know my previous response wasn't very helpful, lol. Maybe smoke test the system for leaks? I'm guessing the pressure release solenoid on the CAC because this sounds like a noise a blow-off valve would make. The rubber seal on those valves is known for tearing. Does the sound vary by acceleration rate? If you're accelerating quickly vs slowly, does the pitch or likelihood of hearing the noise change? That might provide a clue. Here's a video about the part:
Informational video of the 3.5L Ecoboost turbo blow off valve, including electrical diagram, how know if your is good and how to remove/replace.
youtu.be
Thanks for the ideas.
On my vehicle, the sound occurs at low engine RPM, but at various speeds. It never occurs while braking or during quick acceleration, only with a somewhat steady speed and when I lift my foot from the gas pedal.
I can start the vehicle and drive away slowly, and reach 20-25 mph, then lift the gas pedal as I approach a stop sign. The noise occurs.
I can be driving a steady 50-55 mph on a level roadway, and lift the gas pedal as I approach a red light (no brake apply). The noise occurs.
It also occurs at other speeds, but not during acceleration - only a steady speed then a pedal lift.
I did examine the blow off valve location and piping - and there appears to be no damage or breaks.
I’m leaning toward the degas bottle, as it is on the left side and high in the engine compartment - and when lifting the gas pedal, the RPM’s drop and cause a coolant surge.