Yeah so on the way to the UCLA game last night, after the car warmed up, I started hearing a whoop sound coming from the back I thing. This is the second time I heard it doing this in the month I've owned it. It happened under some acceleration and sounded a bit like the beginning of a police siren. Not every time though. Hit accel, one whoop, that's it. 2003 BTW.
Probably the fan for the battery. Maybe the bearings are going, but that is behind the driverside rear seat and doesn't run a lot of the time until batteries are hot.
We have had the same "woop" on our 2003 w/ 180k on it. Glad to hear we are not the only ones! We have been hearing it 6 months and maybe once every 15 days or so. We thought it might be the radio, but never have pinpointed it. How could I check the battery fan? I tried googling "Prius twerp" a few months ago to seek assistance, but the results were all about twerps that drove a Prius...lol.
revising my earlier report. The "Whoop" is happening when the gas engine starts. I initially thought it happened under acceleration but today, stopped at a traffic light with the A/C running, the gas engine kicked on and I heard the whoop. It does appear to be coming from the vents above the back seats. So Joe's idea that it might be the fan/bearings sounds consistent.
