@rexeto93 possibly poor solder connection. You could try and resolder the speaker. If that does not fix it replace the speaker by soldering a new one form places [https://www.injuredgadgets.com/catalog/product/view/id/8231/s/loud-speaker-for-lg-k7/category/893/|like this] or even [https://www.ebay.com/itm/NEW-OEM-Metro-PCS-LG-K7-MS330-LS675-Original-Ear-Speaker-Audio-Earpiece-Part-/262672379917|from here], in place.