As per title; check your rear subframes.
I knew the rear one on my car needed a bit of TLC when I bought it, but it was worse...
Especially the horizontal bits were quite severely rusted one of the sides I chiseled off plaques of 1mm.
Previous owner had sprayed underseal (tectyl) over the rust for which there should be severe punishment.







Checked all areas for weak spots, fortunately got it in time.
I have given it a multi stage anti corrosion treatment and now looks much better.




Planning on doing the rest aswell in future but didn't want to wait and did it on the driveway.

Basic message:
Have a look when you have got the wheels of and catch this problem in time.