how good are you at diagnosing a problem??

[Kryton]

ok, this isnt a "I need help....whats the problem" type thread, the problem has been found and solved.
this is a thread to see what you believe the problem to be, to see if you can solve a problem with the given info, to see if you would have had to pay someone to fix your car or if you would have wound up dead.
the answer will be given at some point in this thread.

the Car:
03 BA Fairmont.
150000
serviced, running smooth.
new front tyres last week.
brake pads need doing in around 10000km according to Ford.
small amount of BA brake shudder.
no other faults........till 2 days ago.

the Facts:

2 days ago: knocking sound occasionally occuring very faintly taking a left hand bend.
cant replicate, cant distinguish front or rear of car.

Yesterday: knocking sound becoming more evident more often. also getting louder. seems to be coming from the rear of the car, yet occasionally seems like the front. cant feel it in the steering wheel.
knocking sound is a "knock....knock.....knock...knock...." not a swoosh sound.

today: on the highway to work, 30km @ 100kmh. ok, now its really bad. definately from the rear of the car. sounds to me like its from the drivers rear. this is bad, it does it in a straight line (most times), it does it on a left hand bend, it sometimes (but not often) does it on a right hand bend. if i slightly swerve the car so the weight is on the right side it is really bad and really loud.
it also does it when i am braking. if i accelerate, the knocking stops. this is the case at any speed. as soon as i get off the accelerator, the knocking is back and its bad.
this isnt the greatest thing to hear doing 100kmh either. i have visions of my wheels falling off and crashing.

ok, these are the ideas i have had today:
a CVD: possible, dont really know what they sound like when they are stuffed.
warped rotor and very little pad left allowing the CALIPER to be hit by the rotor.
possible but it would have to be really warped. i was expecting to have boiled brake fluid and a car fire at work. car didnt catch fire. warped rotor and very worn pads arent really making 100% sense to me. still possible though.
a blown shock/shock rubber. maybe, but not likely. the roads are bad, but they arent that bad enough to be that rough. hit a few potholes to eliminate this and ive eliminated the shocks.

other than that, it had me stuffed. i knew it wasnt the diff, it didnt do it all the time but its did get worse and more consistant over a 2 day period.
this is a sound, that if you hear in your car, you know its serious, you know you better get straight on to it, you know this could end up killing you.
the best way i can describe this sound would be to go get something made of heavy solid steel and hit it with a hammer.....thats the kind of sound it sounded like in the car.

what i have described is what I heard, what i believed, what i tested while i were driving. there is a very good reason i havent just got up and said what the problem was, everyone should know exactly what the problem is if they hear it in their car. it WILL save your life, ignore it and you will find yourself wishing you had have had a shot at diagnosing this thread.

take the time, have a good think about it and see what you come up with.