Car revs at speeds of 60mph or higher on highway.

What is your question?

Recently bought the 2002 Ford Escort SE, thought it was a good car. Today on highway at speeds of 60mph or higher it maintained a revving sound under the car like it was straining. If I pushed harder on the gas I could get it to 65 or 70 but it still made a revving sound like it was straining. Is this just a design flaw or an annoyance of this type of car or do you think there is a mechanical problem? I recently asked a question on this site about a strong vibration when the car idles - I found it was a design defect of this model but not a mechanical problem. Appreciate any advice, I really need this car to be ok so I can drive to work. Thanks.