Been driving for about a week now. I notice when I park and kill the engine, as soon as a lift my foot off the brake pedal I hear a deep “thud” coming from the back of the car.

 

any idea what could be causing it?

Put it on Jack stands, grab a buddy and start investigating. 

On 5/21/2023 at 2:09 PM, MM569457 said:

Been driving for about a week now. I notice when I park and kill the engine, as soon as a lift my foot off the brake pedal I hear a deep “thud” coming from the back of the car.

 

any idea what could be causing it?

Does it still have drum brakes?

Yes it does. They’ve been rebuilt.

Have you had a chance to get it up in the air?

3 hours ago, MM569457 said:

Yes it does. They’ve been rebuilt.

You might look at the rear brakes, the diff, and the half shaft u-joints.

I haven’t looked way back in thread is this an auto or manual car?

Manual. 

On 5/21/2023 at 2:09 PM, MM569457 said:

when I park and kill the engine, as soon as a lift my foot off the brake pedal I hear a deep “thud” coming from the back of the car.

I'd see if the noise is from the brake system alone or if it has something to do with the suspension being loaded.  In other words, does it make the same noise if you press the brake and lift your foot, stopped, over and over again?  Or does it only make the noise when you've rolled to a stop with the brakes on.

Probably the second.  Which implies that something in the rear has a load on it, that is released when you let the brakes off.  First thought is the top of the strut in the tower.  Or a sway bar, or a control arm bushing.  That's three thoughts, but they're in order.

I'd have a friend watch the rear wheels while you put the car in reverse and forward and move back and forth.  Hit the brake a few times.  Something will show.

Edited May 25, 20231 yr by Zed Head
+ ed...eeeww

You mention sway bar…. The mounting brackets broke and we removed it. Wonder if that’s the culprit

I wouldn’t think that would be an issue. 

I'll get back to checking it out. Currently out of country. Car is under stored under a car cover with battery disconnected. I was told it could be a mini-misfire.