I got some replies from the W166 GLE forum (non-AMG), and a few members said that it was related to a possible bearing issue in the firewall. I also found a service bulletin after more googling last night where the W164 ML had the same issue (or at least what appears to be the same issue). Based on this, I'm gonna bring my car in and mention what I found and what others told me, and I'd recommend you do the same! From what the internet has told me, it doesn't sound normal at all.
Last edited by IrAg166; May 21, 2019 at 10:06 AM.