On the 9thgencivic forum, there is also a thread about a popping sound in the seat. I have it too. A guy took pictures and it seems like the spring holding the plastic lumbar support rubs / gets caught. Most people say it goes away after a break in period. Mine still does it at 20k miles but a lot less and with less force.
I wasn't worries about it at all until I saw this thread (not that I'm too worried now), but a broken lumbar support doesn't sound too good. I see two options:
1. If still under the 3-year warranty, and if broke, simply demand the support to be replaced. If they deny, go through Honda Corporate.
2. Just order the lumbar support from the online part stores and replace it yourself. The cover of the seat just comes off with a zipper. All seat components are sold on official and unofficial Honda stores.