is this chattering/squealing noise at slow (<10 mph speeds) w/ICE off normal?

My 06 Prius intermittently makes a sound that can only be heard w/the windows down at very low speeds w/the ICE off. It's most easily heard if you're next to a wall (to help reflect the sound) like at a drive thru and I think if the ICE were on, it'd drown it out. I don't have the AC on at all (HVAC's not in auto) and I'm not on the brake pedal at all but am sometimes accelerating lightly. I'm going straight as well.

It's not the electrical whines associated w/the MGs. It sounds like a series of irregular squeals/squeaks from the suspension.

I took it to Toyota Sunnyvale at ~35K miles and they couldn't repro it (it was too noisy in their service bay to hear). They also said they spent a bunch of time driving around the neighborhood listening for it. They said they tightened some suspension bolts anyway, just in case. Of course, when I got the car back, I couldn't repro either. .

I'm at 45K miles and have been hearing it again for awhile but nothing bad has happened. I've attached a recording. You'll probably need iTunes to play it back. Sorry for the zipped .m4a file but that's all my iPhone 3G could record. Listen only for the squealing type noises. Ignore the knocking noises near the end. I was at a drive thru at the time.

My attempts to get a better recording in a parking structure were to no avail today (wind noise, fans in the garage, etc.)

Is this "normal"? Something serious?

FWIW, I've never heard such sounds from my mom's 07 NAH. My employer has a large fleet of 2nd gen Priuses as shuttles (to take employees from building to building) and I've happened to catch one making the exact same sound under the same circumstances while standing outside.

 

I played my hard to hear recording to the service advisor at Kirkland Toyota on Monday and he felt that it might be sounds from the inverter and likely was normal. He said if it were his own car, he wouldn't worry about it. Their service bay was also WAY too noisy for me to even see if the problem was repro (in front of them).