My 2001 Expy EB with 5.4L engine was leaking gear oil 3 weeks ago when I was out of town. I took it to a local mechanic who said he changed the oil and replaced the pinion seal. After about 300 miles, I heard a roaring sound from the rear end, and when I checked the oil, it was low (could barely reach it with my little finger).
I decided to remove the oil rather than top it off, and I found that it was black colored and had some tiny flecks of varnish looking stuff in it. I now know that I should have removed the diff cover and cleaned it out, but I just refilled it with synthetic oil plus an additive. It didn't help the noise at all, and I believe the mechanic took this woman for a ride.
The noise sounds like an airplane engine winding down, and it only occurs when I take my foot off the accelerator. At least, I can't hear it if it occurs while I'm accelerating. I've never worked on a differential, and after reading everything I can find, it's beyond my expertise.
Am I right in assuming this is a problem with the differential?
How much should I expect to pay in the Houston area?
How do I find a reputable shop to do the work?