I had to send back my original phone when it got stuck in a bootloop due to me being an idiot and removing something I shouldn't'a. Right out of the box, the refurb they sent me, the sound from the external speaker was like about half as loud as my original one, with all the volume settings all the way up, as well as sounds coming through the headphone jack. Annoying, but I could live with it. It almost sounded like it lost a channel somewhere somehow; i'd get sound in both ears, but if there were stereo effects i'd only get one side. Anywho, about a week after I got the refurb, I was having issues with the usb/charging port, where it kept telling me that the battery was too hot and it would shut the phone down. If you tried to start it back up, as soon as the home screen came up it would have the same message, and the phone would shut down again. The only way I could get the phone to work was to leave it plugged in all the time, though there was a ? in the battery status icon and the lock screen would tell me to plug in the charger. I'm also pretty sure they didn't clean it somehow, when I got Facebook notifications, it would play All Apologies by Nirvana, and I never put that on there myself. I took it back and the sent me another refurb, but this one's working fine so far.
So, to make a short story long, it's a good possibility that you got a crap refurb if the fixes the other people told you about aren't working for you. If that's the case, you can try to send it back again if it's still under warranty, but as it isn't a critical issue I don't know what they'd tell you to do.