I doubt it is.
Whilst I'm not familiar with the pezo element in the HP42S specifically, I have some experience with these in other calculators and other devices.
Depending on changes in manufacture, resonances can be created at certain frequencies, leading to buzzing as some part of the case vibrates.
The mounting of the element may also have changed between different eras of manufacture leading to a different coupling to the case or internal components.
The pezo element itself may have changed.
The pezo element may have become loose.
None of these seem to suggest a real problem to me.
If you want to be really sure, complain in writing to HP, asking for a reply in writing. If they say nothing is wrong (most likely) and later on this vivbration causes some problem, go back to them and claim a free calculator (maybe) because they supplied you with a faulty one. You have proof that they were informed, and proof that they said it was OK.
The above may not work, but it's a reasonable shot. Your local consumer laws probably deal with goods that are faulty when purchased. If you've got proof -- so much the better.
But honestly, I don't think there's a problem.
