Loud Resonance Sound

[fordman2021]

Greetings everyone. I recently traded in my Ford Flex and purchased a 2018 Expedition Max Platinum so I’m new to the forums. It drives and rides great and we really love the car so far. I’ve run into an issue and hoped you all could help. Last last, I noticed when slowing down a really loud resonance sound that got louder and louder and then randomly disappeared. It almost sounds like the hum you hear from a 4cyl Honda with exhaust at a distance. It only happens when the foot is off the gas and around 20-40mph. As soon as you hit the gas, it disappears. I turned off the radio thinking it was a sound from the speakers as it sounds like when you get feedback from a microphone near a speaker. Today, it’s been far worse and happened almost every deceleration between the aforementioned speeds. My cell phone picks it up slightly but in the interior, it’s so loud you can’t hear the person next to you to paint the picture of how loud it truly is. My expedition has 39,000 miles. Remember, this sound doesn’t sound like much on the video but in reality, it’s almost deafening. Please help!

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[allaneyre]

I had something like that in another car, turned out to be the u-joints on the drive shaft. Only happened when off the gas as you're not applying torque from the engine through the shaft into the drive wheels. Would come and go as I went from highway speed down to a stop. All depended on the speed of the shaft and the vibration. Also, check if it comes/goes as your turn while slowing. If it does, likely wheel bearings.