I have a 2003 Dodge Neon that I bought almost a year ago. Ever since I bought it there has been a humming noise in the rear end that only comes when; 1. there is weight in the trunk or back seat, 2. hitting bumps, 3. turning either direction. Last night I replaced both rear wheel bearings and springs and struts and it's still making the noise! The humming pitch gets higher with acceleration and lower with deceleration. I am stumped, someone please help!

 

Well I know when RWD vehicles do that it is a result of the rear gears being stressed, damaged, or improperly set up which causes a whining sound. I'm actually not sure how rear axles are set up in the Neon or FWD's for that matter, but if it is the same way just with power going to a different axle you may need a rear end rebuild. Gears will probably cost $100-$300 I would think + labor to install them. I wouldn't recommend it as a DIY job because if they are not installed correctly you'll have the same problem if that is what it is, again, not sure if that is the problem but it's a possibility.