Foundation concerns with 40 year old home
Floor bounce is often a factor of the spacing and span of the joists. Assuming you are in the US, there was a time in the 70s when the building codes were still based on the pre-WWII lumber strength data. But after the baby-boom era in the 50s and 60s, most of the old growth trees were harvested and lumber was coming from new faster growing trees that were not as strong. Eventually the "Floor Joist Span Tables" that are used in the construction industry were updated to reflect this, but the lag time meant a lot of wood frame homes built in the 70s have more "bounce" than older ones or newer ones. It's not necessarily bad, it's just different than you might have experienced in a newer or older home. I have a home built in 1971, I noticed it the day I toured it before buying and I researched it, thinking that the home was defective. But the spans and spacings were correct, for the time it was built.

The vibration from the slab and the cracking may be due to the type of soil you have. Clay soils tend to change a lot each year as they absorb water in the winter and dry out in the summer. My house is on California Adobe soil, in the winter and spring I can feel vibrations coming from transformers in a utility substation 1/2 mile away, but by June or July, I can't feel them any more.