I have a sound that seems to be coming from behind the dash on the driver's side. It occurs at WOT only and it occurs in 2H only (not in 4A at all). It sounds like a bunch of keys dangling from a key ring and being jingled a little and the sound lasts for about a full second. At first I thought it sounded a little like the buzz from an electrical issue but it sounds more mechanical. As I kept thinking about it, I thought maybe detonation but it's too soft and doesn't seem to be coming from the engine bay. I don't have coins lying around in the truck to rattle and it only happens at around 5K RPM give or take 500. I took it to my Ford dealer and the shop foreman rode with me an heard it himself. He thought it was a check valve but didn't seem too confident. He had the tech replace the check valve. Didn't do a thing. Haven't taken it back to him yet. I've read the vacuum check valve and "grinding problem" posts but those don't seem to be the issue. If you have any ideas about what it could be, let me know.
Not sure, but can confirm the vacuum solenoid sounds longer and like one of those old party spinners, duller sound, and last longer. It also with windows down almost sounds like it starts on one side of truck and travels to other side over Maybe 10 seconds. Sounds different from what your chasing. Only other note is I had a bug shield come loose on front of hood and chased in the dash area for weeks till figured out sound travels easily in this truck. I suggest a good look over in the front grill area. The 5k could just be resonating frequency coincidence.
Thanks for your thoughts. I did a video but the sound I'm hearing is drowned out by the other sounds in the cabin at WOT (mainly the engine). The sound can be heard in person but not with the video equipment I have at my disposal. Again, if there is anyone in the central area of NC that is good a figuring out these things and you're willing to take a listen, let me know and maybe we can work out a convenient time for both of us to meet.
