23-12-2018 08:03 AM in
I had the same issue. Later on, I figured out that it was the speaker been blocked by melted chocolate. It happened when I put chocolate in my pocket where my S9 was there as well. I turned off the phone, cleaned it using damped cloth with clean water. The volume is back!!!
31-12-2018 09:56 AM in
I'll be returning my 2nd S9 for girlfriend today. In call volume barely audible. Talked to an intelligent tmo rep/tech support after signing in with a new similar and he thinks possibly it's something to do with the backup software after installation. Lasted 2 weeks on the 2nd phone and then in the middle if the call, bam, the volume dropped.
Only option is to do all new install instead of from a buckup/restore.