I know this post is really old but has anyone actually figured out what the problem is. My 2004 Automatic has the same high pitched whistling that is coming from the bottom rear of the vehicle. It is very noticeable at hwy speeds and only goes away when you accelerate or take your foot off the gas. It still makes the sound when the cruise control is on. Basically whenever the accelerator is compressed or held constant.

My mechanic said it could be a lose baffle in the exhaust and the sound is the air squeezing by and causing the whistle. Or weather it is the rear axle both options sound expensive to fix.

HELP,

thanks