It's the most likely and cost-effective remedy for them. Why redesign and replace the entire chassis (my quick assumption) when a shim will do? They needed it thicker at a certain point to reduce the noise, so a fix was incorporated into the manufacturing process. So, yeah, there was a change, but it was only changed where it needed to be changed, with a simple addition that would repair the issue. The bottom line is that the noise issue was fixed and any of the SDS200 scanners now sold (current stock) should be without the hum. What would be nice for future buyers is a serial number cutoff so you would know if the SDS200 you are buying is before or after the noise reduction addition.
JD
kf4anc