Fluttering noise from front end, only when coasting

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Our 2010 Sienna LE 2WD has recently developed a "fluttering" noise (a little softer than a clatter) that sounds like it's coming from the front driver's side wheel area. Noise appears only while coasting. Most easily heard between about 25 and 45 MPH. If I apply the accelerator, noise stops almost instantly. The noise is not as loud, in neutral while coasting. The flutter is far faster than the rotation of the wheels (e.G, not a rock in the tire, etc.). The speed of the flutter does vary somewhat with the speed of the vehicle (slower speed = slower "flutter"). The "flutter" is very regular - like a muted version of what you'd hear when you put a baseball card in your bike spokes as a kid. Occurs regardless of uphill or downhill; cornering and braking don't change the noise at all. Doesn't happen in Park. Pulled front driverside wheel; nothing unusual noted. Recent work: full brake job (all 4 rotors replaced+new pads), new front tires, front alignment. Noise started ~2 weeks afterwards.