I have a 2021 ST with just shy of 36k miles. For the last 5 months or so, I've had a noise that sounds like it's coming from the passenger rear end. It only happens when I'm in reverse, such as pulling into my driveway or a parking spot, and usually after a short drive. It's a single, solid clunk. BUT, it doesn't happen every time, maybe half the time. And not when the service tech is in the car and I'm trying to demonstrate. My local Ford dealership has had it twice and replaced both rear shocks, and I called them again this morning after just getting it back, it did it when I got home from work last night and again when I arrived at work this morning. (The service manager drove it himself and made it do it 3 times, so he's got firsthand experience.) They say that everything under the car looks good and is in spec, but this can't be normal. What could it be??