To be honest, I don't understand the difference between the two either. I was told they both are incomplete or with errors, but I've looked at both and I sincerely can't see anything wrong on any kind of serious level. If there are errors with the squad file they made, it's either so micro on bench players I don't know or in things like haircuts that I couldn't care less about. I'd say just go with it. The patch plays great as it is now. That being said, I only play England, Italy, and Spain and all only premier leagues. My bigger concern is the sound skipping I get with this patch.
As far as your squad file question from FIP, as long as they both use the same DB, it'll work. Just put it in your documents folder. If it says it's damaged, then you can't use it. But again, if you're even willing to use last year's file and do only major updates, you'll find these work fine.
I started a new career yesterday with the squads that are included on the v4.1 package.
So no additional "updated" squad files.
I have no issues to report up to now.
Also, did not encounter any issue with age of young players that I did with the Oct 6 optional squad file.
So until V5 comes out I'm good for now.
In any case, regarding your sound issue.
I have a couple of suggestions that may help in case you haven't tried them.
What FPS setting are you using in FIFA 18 settings? Is it on unlimited?
What is your screen's refresh rate?
If it is 60fps, then adjust the setting it to 60fps or to match you screen's refresh rate.
There could be an imbalance on your PC between with graphics and sound.
The mod may require more juice from your PC and it may not be able to handle it 100% under your current settings.
Lowering some settings may help.
Also does this happen on windowed or full screen mode?
Try the other options to see what happens? I have issues with Full Screen mode so I use windowed because of my multiple screen setup.
Are you using multiple screens?
Turn em off except the main one.
In the fifa settings what DirectX setting did you opt for? Try auto or 11 if it is currently set to 12.
The audio tab. User stereo if set to anything else.
How is the sound generated on your PC?
Motherboard, audio card or integrated into your graphics card?
Assuming you are using an audio card.
Plug your speakers to the motherboard to see what happens or basically use another sound source to test.
Make sure your firmware and software drivers are all up to date.
Could be simply a driver update that is needed on any of your PC components which can be easily done through the device manager.