Greetings, 2011 Prius II, 170K miles. One owner, bought new in 2010. A few months ago, started hearing new hum. Appeared suddenly after routine maintenance (oil change and spark plugs), although may be unrelated. Hard to describe, but the closest I can think of is rough truck like/sport exhaust /failing muffler type of low pitched noise. 1. Speed related. Appears at about 30mph and peaks at about 50mph. Easy to hear as the car is usually very quiet, especially on battery power. 2. Can be heard even with ICE off, on battery power only 3. Cannot replicate by revving the car in garage while in parked mode 4. Worse when turning right then left on high speed Went to 2 independent mechanics locally, one cared for my car for a while, the other was recommended by multiple people in the neighborhood, with 100s 5 star yelp reviews. I had bad experience with 2 dealerships near me in the past, so stopped using them a few years ago. Both mechanics said the same thing. First recommended new tires, as my were worn out. I did that, with no changes. Then recommended wheel bearings. I did that as well, but no change. Noise is still there Now I am at a loss. Looks like a mechanical issue to me. I drive out of state, long distance, and concerned about something happening in the middle of nowhere during freezing weather. Looking for any ideas one might have as to the possible cause(s). Thanks very much
