The audio for the LIRR M7 has the same audio as the Metro North M7A (horn, acceleration, and deceleration)
That's not a bug. The previous m7 audio was really bad, go on YouTube and look up tsw2 lirr and have a listen. The m7a used audio that sounds like the real train. If you even go on YouTube, you'll know that the audio on the m7 is the same
Well horns aside, they are pretty much the same thing. They have a different gearing ratio, but the traciton motors and everything else is pretty much the same, so no wonder they sound the same.