My 03 Galant 4cyl makes a knocking sound in the rear of vehicle when breaks are applied. I had breaks checked and they are fine

CHECK OIL LEVEL, SOUNDS LIKE A ROD KNOCK, CATASTROPHIC FAILURE

This fault is a bit srange, when you apply the brake pedal you here a
"Knocking" noise from the front of the car, alternating from one side to the other, the cause of this is a bad earth in the rear light clusters,
which results in the headlight motors activating "Jumping" thus causing the noise, solution is to clean the conections and conecting
blocks of the rear light clusters in extreme cases change the rear light clusters but a good cleaning should fix it hope this was helpfull

flywheel could be loose. If you have bottomed car out any time recently, transmission dust cover could be making contact with torque converter or flywheel or both. If your performance is fine could be exhaust system, (some part of it toward the middle to rear), is making contact with underside of vehicle while idling or applying throttle. Questions: Does the sound go up and down with throttle? At any time while running does the sound stop altogether? Let me know and we'll have u an answer in no time. thanks

check the upper suspension mount in the mudguard at the top of the shock absorber. It is a large rubber mount held in by 3 bolts. They have a habit if breaking and allowing the shocky/steering mount to move around. Test by jacking the car off the ground and watch for down wards movement of the rubber. I have known then to allow the whole unit to drop out .

Just a stupid little suggestion, check that the exhaust in not knocking on something - check all the exhaust suspension rubbers and shake the exhaust system around to see if you cannot repeat the knocking.

I own a 2001 Windstar. Your noisy brake problem could be nothing more that new brakes being broken in. I have done many brake jobs on my 2001 Windstar as well as other vehicles that I have owned. To prevent this problem from occuring, I apply a thin film of Disc Brake Quieter directly to each brake pad during the installation process. This quiets the brakes during the break in period. I hope this helps.

It sounds like a bad earth connection in the vehicle rear wiring loom. Check the earth wire that runs from the globe sockets in the light units and any connectors in the wiring loom near the light assemblies as well as where the earth wire is attached to the body. If necessary, remove, clean thoroughly by removing any corrosion or paint and re-attach securely.

Replace the turn signal switch. Bad contact inside causing a crossing of the circuits. When the turn signal is applied it should open the brake light circuit allowing for just the signal to work. Doesn't sound like the switch is doing it's job.

More than likely it is your control arm, or a strut. It only does it when you apply the breaks, i think it is the control arm. Need to get fixed as soon as possible.

Does it sound like it's coming from the fuel tank?