Yes, the only people you need to worry about are Ford and Maybach. They might be able to lay claim to the sound their engines make as being theirs. If the hobby goes that route through litigation, what a sad world we live in. Good thing these engines are all older designs from 60 years ago.
Correct. The engine sounds themselves are not under copyright (as long as Ford and Maybach have not protected them under copyright laws). Harley Davidson does have their engine sound under copyright.
Tamiya's
recordings of those tank engine sounds
are protected by Copyright law.
As for Panther G's accusation that we are using recordings under copyright, it could be considered as defamation of character aka cyber-libel. There are people who are sued over such comments (
that is not a threat, just a fact).