Do this simple test:
Shifting soil or heavy traffic above the line can cause older pipes (clay or concrete) to collapse or sag. 1.3.4 How to Diagnose and Fix
Cooking oils poured down the kitchen sink cool and harden inside the pipe, narrowing the passage over time. 1.5.1
If you have access, check the inlet baffle inside the septic tank. If you see toilet paper or scum blocking the pipe entrance, you can sometimes clear it by breaking apart the debris with a long pole . 1.4.8
Have your tank pumped every 3–5 years to prevent solid waste from backing up into the inlet pipe. 1.1.1
If you continue to hammer at a solid object (like a piece of broken concrete or collapsed pipe) with a snake, you risk: