Hi,
You may wish to check the following setting in your phone
Voice Clarity
This feature allows you to set the phone to automatically adapt to noisy environments by
adjusting the audio levels to improve speech intelligibility.
1. From standby mode, press OK
[MENU].
2. Press Key 9 Settings & Tools.
3. Press Key 6 Sounds Settings.
4. Press Key 8 Voice Clarity.
5. Use the Directional Key to scroll to On or Off, then press OK
See page 83 of the user guide. Here is a link:
http://www.lg.com/us/support-mobile/lg-LGVN251