This bug has been a thing for as long as I can remember, but I don't think anyone's reported it yet.
Thanks for reporting!

Here are some videos demonstrating this bug. Looks like the train sound doesn't pause any time the Philly erect stage is used.

Normal

Erect (bugged)

Seems like it's very easy to fix, these functions are in phillyTrain.hxc but not in phillyTrainErect.hxc

         public override function onPause(event:PauseScriptEvent) {
		super.onPause(event);

		// Temporarily stop ambiance.
		if (trainSound != null) trainSound.pause();
	}

	public override function onResume(event:ScriptEvent) {
		super.onResume(event);

		// Temporarily stop ambiance.
		if (trainSound != null) trainSound.resume();
	}

Just wanted to add to this issue that the same thing happens with the lightning strikes in the new difficulty and pico versions of the two Skid and Pump songs.

Hm, sounds like something @NotHyper-474 could add to the PR

I may have come up with a better solution that automatically pauses/resumes every sound instead of having to manually handle it through the stage script. When I have battle-tested it enough I might make a PR on this repo.

same thing happens with the lightning strikes

Now that I think about it you might be talking about the lightning itself and not the sound, althought it happens with the sound as well, perhaps a bit out of scope for that PR.

I was talking about both?

Anyway, I think I found a way to fix both, although I'm not sure if it's safe since it requires pausing every currently active tween, whereas the original code only pauses some of them.

At the moment it doesn't seem to break anything, but just in case I'll still make the PR only pause sounds.

They also need to fix the issue where the train sound occasionally doesn’t play on the normal stage.

Same thing also happens in Mommy Mearest songs with the car - except that the car sprite in the normal versions of the song actually pauses, though the sound doesn't, but then disappears once the sound effect finishes playing while the game's paused.

This issue is a duplicate. Please direct all discussion to the original issue.