My family moved into a house about 7 years ago. The house was about 10 years old at that point. It has a 2 stories and then a basement (sort-of finished) and garage. The garage is under the house, specifically, under the dining room and kitchen, with my parents' bedroom on the 2nd floor above the dining room and kitchen. On the north side of the house the 1st floor is only a few feet above ground, but on the south side, which is the garage side, the ground is level with the floor of the garage.
When we first moved in we noticed an odd sound coming from the dining room at night, kind of a popping sound. I wasn't really concerned about it until a couple years ago when we noticed a long crack in the exterior brick, running from the window in my parents' room, to about floor level of the dining room. (I've read some things saying a crack could be due to a garage door lintel sagging, but the crack doesn't reach down to the garage door, and it seems to start at the top because it is wider up there.) I've also noticed that the dining room 'pop' is now a MUCH louder and sharper sound than it was when we moved in.
This morning I was in the garage and since I was down there, decided to examine the (unfinished) ceiling. (I actually know nothing about construction, so bear with me here) It looks like the supprt consists primarily of long wood beams, about 6"-8" tall, running east/west that are braced by shorter pieces of wood. The shorter pieces are attached diagonally, with 1 end nailed to the top of the beam and the other end to the bottom. However, they don't look right to me. They are not uniformly placed; some of the diagonal pieces are flush with the bottom of the long beams, while some are several inches above the bottom, and pretty much at every point in between, and there doesn't seem to be any pattern to the differences. Some of the diagonal pieces are completely detached at the bottom. They are also not all the same thickness. In other words, it looks to me more like the things that I used to build from scraps in my grandfather's woodshop, and not like a professionally built structure. Also, one of the long beams is breaking - right under the dining room. As far as I can tell, this woodwork is what is supporting the floor above. It attaches to the brick on all sides and I assume is transferring at least part of the load to these brick walls, but the fact that parts of it in the middle are no longer sound makes me very nervous. For several years I have suspected that the "house settling" sounds from the dining room are actually the sound of nails moving and breaking and/or wood cracking or breaking underneath the dining room, or some other kind of structural failure.
Basically, I'm afraid the garage ceiling is going to fail, which would probably take out the dining room and my parents' bedroom as well. My family does not take this seriously, but it's not like they're construction experts, they just either don't want to deal with it or assume the building must be safe or it wouldn't have been built - but I can't agree with that; soon after we moved in, the floor of my parents' bathroom gave out b/c a leaking pipe had weakened it, and had to be repaired. Also there are matching cracks in the wall on both sides of a room that juts out from the kitchen, as if that whole room was a last-minute addition that isn't properly supported. Anyway...I was wondering if anyone could tell me if this really does sound like it could be serious, or am I just freaking out over nothing? I know people can't fully assess a situation over the internet, just hoping for a recommendation or first impression. Seriously, this is affecting my ability to sleep at night.