Volvo Repair: 98 volvo s70, volvo s70, signs of trouble

Question
recently purchased it with 116k miles.  coming home one night i decided to turn off the radio and listen for any signs of trouble.  when the car is traveling between 45 and 55 miles per hour i can hear a rumbling sound coming from the front end.  some suggested replacing the tires, i did but sound still occurs.  one mechanic suggested i replace the hub bearings.  this is where i am right now.  if I replace the hub bearing and it still makes this noise, what else can it be.  hubs and labor are expensive.  could replacing the hub bearings really solve the problem or can you think of something else? thanks in advance.

Answer
Andy, if those hub bearings are bad, you will be able to hear them.  They are really loud when they do go bad.  You can mistake the noise either.  Sounds almost like a jet plane going down the runway.  How bad is your sound? and what tires did you put on the car?  Roger