I have standard wooden stairs that use wood blocks and wedges and a stringer at each side. The wall-side stringer makes a light cracking noise as we walk up and down and it is persistent. After a few walks up and down it improves but a bit later returns. If I push the stringer with my palm I get the same noise. I have been spraying the stringer and nearby tread and riser with fine water spray with very limited success. A friend says inject foam up in the gap (1/2\\\") between stringer and wall. I wonder if that is in any way \\\"dangerous\\\" I have re-fitted all new blocks between riser and tread which made the stairs very solid but still I get this cracking noise. I also tapped in all wedges. The stairs are 120 years old but I need to fix this as it sounds so bad.