I have an 05 LL Bean Wagon H6 automatic with 225,000 miles on it. I just got the car from original owner thru original dealer this December. I have developed a very low pitched vibration/rumble that appears ONLY when I am on the throttle. Driving down the highway last night I experimented. At 60 MPH and foot on throttle it was making the noise. As soon as I lifted off the gas it went away and was quiet, but still at same speed. That would pretty much rule out tires and maybe CV joints. It starts at about 20 MPH. Sound seems to occur between 20-45 MPH regardless of whether my foot is on gas. but at 50-65 mPH the sound goes away less than a second after I pull foot off gas. A person sitting in back seat says it is coming from under middle of the car. Also, I have had an annoying weep-weep-weep sound from someplace in middle when backing up. I have been told it is likely the rear U-Joint or a carrier Bearing. Are these expensive to replace?? Probably dropping the Outback at my local dealer tonight in hopes they can fix quickly. I hate paying dealer prices but my experience is I do not want aftermarket stuff being put in the car. My last used 05 was a disaster after used car place put in after market cats and o2 sensors. Thanks for any immediate help.