You need to swap the back-plates to see if the problem persists. However, if the problem reappears but on the opposite speaker panel the problem may be associated to the backplate.
How many years is “several years” since you have had them? Are they under warranty? It would be very expensive to ship the 945s back to Sound Lab. You might be better off just preparing yourself to do as much diagnostics as possible yourself with the help from the members here.