Most Likely & Relatively Inexpensive:
* Loose or worn suspension components: This is the most common cause. Check the following:
* Shocks/Struts: Worn shocks or struts will allow excessive bouncing and can create knocking sounds. Visually inspect them for leaks. A compression test at a shop will definitively diagnose this.
* Sway bar links/bushings: These connect the sway bar to the control arms. Worn bushings or broken links can cause knocking, especially over bumps. Look for excessive play or damage.
* Control arm bushings: These bushings wear over time, causing knocking and clunking. Inspect for cracks or excessive movement.
* Leaf springs (if applicable): While PT Cruisers generally don't use leaf springs in the rear, if your model does, worn or broken leaves can produce a knocking noise.
Less Likely, but Still Possible:
* Exhaust system: A loose exhaust component can rattle against the undercarriage when going over bumps. Inspect the exhaust system for any loose hangers or damaged sections.
* Brake components: While less likely to cause a *knocking* sound, worn brake pads or a problem with the caliper could contribute to a noise. Check the pads for wear and listen carefully for any dragging or grinding noises.
* Loose or damaged body parts: Something might be loose in the rear of the car (e.g., a trim piece) and rattling.
Least Likely (but potentially expensive):
* Differential problems: A damaged differential is less likely to cause just a knocking sound, but it's possible, particularly if the noise is accompanied by other symptoms like vibrations or a whining noise.
* Suspension mounting points: This would involve rust or damage to the chassis itself, requiring more extensive repairs.
Troubleshooting Steps:
1. Visual Inspection: Start by carefully inspecting the rear suspension components, exhaust, and undercarriage for any obvious damage, loose parts, or wear. Jack up the rear of the car (safely, using jack stands!) to get a better look.
2. Listen Carefully: Try to pinpoint the location of the noise as precisely as possible. Is it coming from the left, right, center, or all over the rear? This helps narrow down the possibilities.
3. Test Drive: Have someone ride in the back seat while you drive over various bumps to help localize the noise.
4. Professional Inspection: If you can't identify the problem yourself, take your PT Cruiser to a qualified mechanic for a diagnosis. A good mechanic can quickly identify the source of the knock.
Don't delay addressing this issue. Ignoring knocking noises in your suspension can lead to more significant and costly problems down the road.
