Gen II Noise while decelerating between 45-55mph

So I've looked around and I can't find anything that seems like this problem.

2007 Prius with 44,000 miles.

I have an intermittent noise that sounds almost like a bad wheel bearing (though it isn't) but only while slowing down (foot off the brake) between 45 and 55 mph. It is not constant - sometimes I'll lightly press the accelerator, let off, and the noise will be there - other times it won't be. It does not *appear* to be getting worse, but I'm stumped as to what it could be. If I shift to neutral at these speeds I can still just barely hear the noise.

Actually, it sounds less like a wheel bearing and more like road noise from cheap tires but only while coasting between 45 and 55 mph. Above and below these speeds I cannot hear the noise at all. I had the OEM tires replaced with Hankook Optimo tires recently and the noise has remained the same.

The noise sounds almost like it is coming from the driver's footwell, but it's hard to say that with any reasonable accuracy. Car has no drivability issues. I've owned it for approximately 13,000 miles and have just begun to notice this in the last several weeks.