A change in sound when accelerating led me on a search to find out what was going on.  Snooping around beneath the S4 revealed this:

Found it!  Fortunately Apikol sells just the bushings for the mount so I ordered a pair to replace the failed parts.

It turns out that there are two versions of this bushing so I needed to order both since I did not know at the time which version I have.  I’ve documented the part number in case this happens again.