A Home Inspector has to rely on what is visible during an inspection. Fortunately, there are many indicators to tell me what might be happening inside the walls of a house. I use a really bright flashlight to scan the surface of walls at an angle looking for ripples or bulges that are not readily apparent. If I spot an issue, I think about the structure of the house: Wood-framed walls?; Lathe & plaster over block?; Steel studs & sheetrock? Every construction type will ‘telegraph’ problems in a different way so you have to know how to read the walls, the ceilings, the foundations, the attic.
So, let’s say we see a slight crack in a bedroom wall. Every building moves over time. The building might settle a bit or the changes in seasons and temperatures might cause contractions or expansions in materials. Is this crack a sign the house is splitting apart? OK, so we check out the foundation for excessive movements, the kind that might be a serious problem. Well it looks good, drainage outside is OK and no interior issues of note. Foundation looks to be OK.
Move to the attic. Is there a leak in the roofing materials, flashings at the chimney, ice dams at the eaves? No, no leaks, no moisture, structure looks good. AH, but there is an air-conditioning unit sitting on joists in the attic. The unit is approximately over the area of the bedroom wall in questions. It is possible that fan vibration when the unit is running might be a cause of the minor crack in the bedroom. I would recomend a servicing of this HVAC unit which will include filter changes and clearing of the condensate line as well as checking for appropriate vibration dampers.
Meanwhile, a spackle and painting of the bedroom wall is probably all that is needed since the rest of the structure has passed the test. As always, we look for trouble but are happy to just find good answers.