2008 Toyota Prius aboiut 45K miles, just did 3Kx2 Cross Country, and now I notice a “roaring” constant sound from about 35 - 50 mph. Seems to subside at higher speeds, although this may just be that the sound is being drowned out by freeway noise (and radio!). Mileage has remained consistent, and no performance issues observed. Maintenance is current. Ideas on what this could be?
Well, I don’t know what a 3Kx2 is, but I suspect that you have a bad wheel bearing or two. Wheel bearing noise does tend to change when you turn and usually be detected by jacking up the car, spinning the wheels and listening for roughness. The wheels should spin very quietly and smoothly.
+1 to Cig’s post.
Other possibilities are an exhaust leak or a worn tire. Some tires get noisy when the tread gets near the wear bars.
3Kx2 = three thousand mile (trips) x2; just saying I recently drove back and forth across US.
I have about 30,000 miles on Nokian WR (all weather) tires. I’ve looked at tread, and really just don’t know, but have my suspicions in that direction. Use a different tire guy than mech, so, I guess I’ll check tires first, then if that doesn’t work, appointment at the dealer (which is surprisingly affordable here in Morgantown!), regarding the wheel bearings.
Tire whine from choppy tires & worn wheel bearing noises can be similar. Tire whine generally increases in frequency (pitch) as vehicle speed increases. Worn wheel bearings often remain the same frequency but get louder with increase in vehicle speed.
If the sound from 35 - 50 mph is there, try swerving (carefully w/no traffic nearby) left, then right. If the sound remains pretty much the same, it’s probably tires. If the sound disappears momentarily when you swerve left, it’s probably a LH wheel bearing (when swerving left, weight of car decreases on L; increases on R.) If sound disappears when you swerve R, it’s probably a RH wheel bearing.
If you have access to another car that doesn’t have these kind of noises (your “good” car"), see if you can find a road whose surface material changes at some point, say, asphalt to concrete. If the “good” car’s tires change their sound going from one road surface to another then try the problem car. If the roaring noise changes as well, then it’s probably caused by tires, not wheel bearing(s.) Do you see where I’m coming from?
If you jack up, say, the RF wheel & rotate the RF tire while holding the coil spring with your other hand & you feel a fine, slight vibration from the coil spring & this scenario doesn’t take place on the LF, then it’s probably a worn RF wheel bearing.
Of course, it could be you have more than one worn wheel bearing.