There is a weird high pitch humming noise coming from under the car in the middle around the driveshaft area or from the rear end I can't pinpoint it because it only does it once I get above 40mph. I climbed under it today to check it out better the only thing visible I could see is a rusty drive shaft other than that everything is clean as a whistle. I need to be more clear about the noise it only does it once I go over 40 mph but if I gain some speed and let it coast the noise goes away until I give it some gas. Iv had this issue from day 1 iv never had a problem it's just rather annoying. Repair shops are very pricey and I'm a handyman so I know I can fix it if I can find out what's going on anyone have any ideas? Could it be the rear end gear is low? The SUV has 128000 miles and is a rear wheel drive V8.