Getting tired of the same old sounds? Same weapons sounds, bitching betty sounds, etc.? Well, Solahma has been keeping a library of sound PAK files in one of NGNG's forums. These include numerous physics sounds (weapons, etc.), multiple bitching betty files (male and female PAKs from UK, AU, etc.), files with sounds ripped from MW2, MW3, MW4, and more. Personally I have been using Kendrick's battle enhancements file (physics) version 1.5 (now updated to 1.8, but not yet included here) for some time and prefer it much more than PGI's sounds.
Here is the sound file link if you are interested. Just place the PAK file(s) in the GAME subdirectory, normal path being "C:\Program Files (x86)\Piranha Games\MechWarrior Online\Game".