I just finished reassembling my 04 G35 coupe's interior after replacing the sunroof, but have now two parts leftover that I'm having trouble identifying. They're identical white plastic blocks ~2"x1"x1" (see image). If I had to guess, I would say they belong somewhere underneath the A pillars. But if they do, I can't figure out exactly where, or what purpose they serve.

I tried looking them up by the number embossed on them (73991AL500), which I would assume is their part number, but found nothing. Any ideas? Thanks in advance!