Noise reduction on 2003 Toyota Echo

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I bought this car from a Nissan dealer who said the car is noisy because of poor insulation. It sounds like a small airplane. Noise increases with speed. was considering adding insulation or bedliner paint under the carpet. Transmission was serviced by dealer and seems to shift fine. Anyone have some advise?
(1) Answer
I would have the tires and/or the wheel bearings checked.
Tires with irregular wear and/or worn/damaged wheel bearings will be very noisy...and that noise will increase with speed.