Noise coming from rear of car.

Sorry didn't mean to say the light stays on all the time but that the 4x4 light has been coming on for a long time, blinks and goes off. It has been serviced right after it came on and regularly since it has come on. I am told by a Ford Dealership that it needed setting after I had a break job, which they did. However, the light did not go out. It is on when I start, after traveling exactly .8/miles it comes on, flashes 8 times and then goes out till the next 8/10th of a mile. Have had it looked at at least 4 different times at dealership and another mechanics shop I used regularly..No one has any other idea [other than resetting computer e.g. after brake job, wheel bearing, etc.], how to 'make' it stay off. Rather that is contributory to this noise I don't know but it seems that the differential would have gone out a couple of years ago if that were the reason for the light. As for the leak...I can't see anything leaking, yes it may be because there is nothing to leak out anymore, only darkness like a 1/4-1/2 moon area around what I think is the differential. I do not see any evidence of leaks toward the front of the vehicle i.e. pinion seal. But then again I am not sure rather the differential is considered the rear end and if that is where you put heavy oil in when getting oil change/service at so many miles, or if it is the differential? I will have to look again to see what the half shafts are you mention, although I don't think that is where i see what I believe is evidence of a leak. It has bolts all the way around it [looking at it from the rear of the vehicle], but I haven't checked to see if it also has a 'drain' plug for changing. I will today and surely let you know. I am the original owner of the vehicle and for it's first 6 years I lived it VT. Is it possible it "could" be that this dark area around what ever it is I have described, could be stained from sitting in snow [can't be avoided in North East Kingdom of VT...], or from the salt et al they put on the roads? I really don't know. I haven't driven it at all since I heard the noise. Perhaps if anyone had been able to give me a reason for the perpetual 4X4 blinking light, if this has caused the problem it never would have happened. The light came on like this in around 2008/9?? Don't mean to be long-winded here but really need help. Trying to explain best way I know how. I have a Ford Explorer I am using for to go to work and the gas here in FL is killing me..I need my Escape. Thanks so much for you help, I hope this gives you more insight. You certainly sound like you know what you're talking about. I think I need to get a schematic of the under coverage of my car?

If your 4wd light blinks 8 times , goes out, and then does it again it is one of your cv axles . look behind each of your front tires where the cv axle meets the break rotor. There is what looks like a gear .(really thin with alot of teeth) It should be tight on the cv axle. It will either have a crack in it or spin freely. I have had this problem twice on the passenger side of my 2005 escape. Relatively cheap and easy fix.

Check the electrical plug in the rear end sometimes when serviced the tech will pull the wires part way out of the plastic holder and now are not making good contact with motor in rear end, push the wires back in. had this problem when changing rear unit if 05 escape awd.

When the front wheel tone rings cause the 4WD or AWD light to flash, the ABS light also goes on.