2002 Toyota Corolla Humming at acceleration

It doesn't sound like a vacuum leak to me. It sounds more like either a wheel bearing issue or uneven tire wear.

Ask her to do this. In an area where it is safe (no traffic), drive the car until she hears the noise. Then, turn the steering back and forth from left to right. Does the sound change? If it does, in which direction does it get louder?

Also, have her check to make sure the tires are not cupped or worn unevenly.

Let me know what you find,

Joe

Thanks-wheel bearing (it was just replaced, so it is free including the labor-this is the second time its been done). Also the Cat. was almost completetly blocked and per the mechanic "peeling apart, completely broken down"-would something like this cause a CEL PO303/PO300-random misfire?

So it was the wheel bearing? As far as the cat, a plugged one could cause misfires from the engine because there is too much back pressure.

thanks-yes it was the wheel bearing-they say it must have been defective part-so they will replace for free on Tues-She hopes that will dissapate the noise

Glad you found it. If they replace it with a good bearing, the noise will be gone. Let me know if you have other questions.