ill go over this as accuratly as possible.. i too am having the rear diff clunk... i should be used to it i own a subie.. but earlier today, i was about to pull in the walmart parking lot.. the clunk turned into more of a faster paced rattle.. and the car died as soon as i pulled in the parking lot.. things to consider..
engine was running fine, and still runs fine..
plenty of oil pressure
not overheating
Transmission did not seem to be acting up
no issues with fuel
and as far as i know.. plenty of air
The sound WAS DEFINATLY coming from the rear
i need help

 

Unless the diff / cv's are dragging very bad, the sound from the rear & the engine dying aren't connected...

Does the car coast fine?

 

yeah.. didnt have any problems after that.. reved in neutral and coasted fine

 

So jack the car up, & check out the rear end.

 

that of course i would have love to have done, but didnt have a jack, and my street was flooded.. so i couldnt have looked at it.. ill look at it at work tomorrow, least ill have a nice dry environment

 

alright.. clunking sound was a ball joint.. how lovely.. after about 3 hours under the car checking and fixing everything needed.. i have decided i made out like a bandit.. for the most part.. minimal rust.. lil under driverside floorpan.. lil under the trunk area and thats it.. two new axles for $110.. thanks to a a friend of mine at a shop.. shocks are in good shape but they will be replaced when i get springs.. aftermarket exhaust that was on the car when i bought it is in good shape, so all good i think..
also added new plugs and wires, new cap and rotor, cleaned out the AFM.. shes running pretty good, but now i have a power draw im looking for and cant seem to find.. possible alternator

 

Ball joint? I think you mean U-Joint as there are no ball joints in the rear.

As for the alternator... take the car on down to a parts store & have them check the alternator output.

 

u joint, sorry your right.. typing while working gets u errors