u/Large-Welder-1428

My 2011 Pro-4X produces a whistling sound under throttle (both in Park and in Drive). The vehicle is well maintained and shows no performance issues. All vacuum hoses, the air intake duct, and the manifold are in good condition. The valve covers are new, so it’s unlikely to be a PCV issue.

Interestingly, the sound disappears every time I remove and reinstall the intake duct. This makes me suspect a small leak in the air box that develops later, possibly as components shift slightly with vibration. The air box is securely mounted with new hardware.

Has anyone seen something similar?