Rental house shifts/settles too much with seasons, bedroom floors with slope (?)

[Jeff Ryan]

Hi, In Muskegon more specifically, to note for seasonality of this. I've owned the house (SFH) for a little over 3 years, rented to the same tenant.

She's noted/complained about 2 of the far bedrooms floors 'sloping' and seems to be with the seasons, worse in the winter than in the summer, where they seemingly go back to normal.  Also, per the images, a crack develops in the kitchen, on the other side of the house where the wall meets the ceiling.  This also showing up in the winter, and the crack closes back up again in the nicer summer weather!    

I went into the bedrooms and don't notice the sloping floors so much just by 'feel' and admittedly haven't put any measuring device like a level to it.  She says she notices it in bed and has to put the bed a certain way (like with head on higher part).

This doesn't seem to be enough of a problem where any part is unlivable or that requires immediate attention, but the main jist of this post is, where would I start or what type of business or contractor could I start with to find out about this?

I had the house inspected when I bought it, and nothing really came to light about this.  The foundation was noted as good, and the foundation in the basement doesn't show any obvious signs of problems that you might typically see with foundation problems.  The basement is full, concrete walls that are very straight.  

Is it some kind of foundation specialist to start with to at least know what it is and know if there is anything reasonable that can be done, a general contractor, or is this something I just write off as seasonal shifting of the foundation that happens with some?  Thanks!!