I got the sounds to work by putting them in the original location (...\Kerbal Space Program\PluginData\MMI_Kethane\sounds) where "echo_deposit.wav" and "echo_empty.wav" are the only files within the directory. All other "PluginData" files should go into "...Kerbal Space Program\Plugins\PluginData\". EDIT: This post is outdated. In context, it pertained to getting sounds from Kethane Mod Pack 0.4.3 to work with KSP 0.20.