There are 4 grammaphones you can activate that I found while doing these searches, they each cycle through I believe like 5 songs. For a while I thought that maybe in a certain pattern they would activate something leading to a key. I also thought it had something to do with the music that the boss zombie plays when he walks around. I found nothing and they do not unlock a key. I don't want to put out the idea that they might have some type of side easteregg involved with them, but It seems like a lost cause.
TLDR: I know about the grammaphones, I don't think you will gain anything from them that is worth the time to figure them out. (If they even do anything)

Hi, i saw your Complete Guide to Return to Das Herrenhaus, and i asking myself if you know about the locations of the grammophones, and if they do something ? thanks

Yo, on your das herrenhouse post for the club key - where specifically is the stamin up bottle? I know you left photos but I dont know where that location is from them. Thanks

:)