My now 10 month old was just like this. I think some babies just don't like being babies and want to be able to do more than they physically can.
Once he started crawling he was so much happier and once he started cruising he was so much happier again. He is now desperate to walk and I know he will be again happier still once he manages.
Before; he was constantly grumpy, doing the whining sound all day every day, needing constant entertainment but then getting bored after ten seconds.
Now he is a completely different child. He smiles so much and laughs so much. He crawls over for cuddles then often wanders off and does his own thing. Don't get me wrong he's obviously sometimes still grumpy but it's nothing like the constant discontent that was making me really stressed and feel like I must be doing something wrong.
Now he often just sits on the carpet playing with his stacking cups making noises to himself and occasionally looking around to check we are suitably impressed with the manner in which he is banging said cups together.
He has also always loved songs and music and often they are the only things that helps when he is upset.
He also hates nappy changes and screams like a banshee. For the last six months nappy changes have been helped by animal sounds and funny voices and singing songs.
He loves making his toys play songs and he bobs his head to the music and smiles and giggles as he listens. In fact he has one toy that he can't yet press properly to make the music so he often bobs his head to tell us he wants it on. It's adorable!
I have stopped worrying so much about rods for backs and things. Most of the time people said it to me it felt like it was just taking the joy out of everything although I have no doubt it was well meant.
Unless it's something that would really be awful to have to continue in the future or is something that would be bad for you/them, I think just go for what makes them and you happy.
I know listening to Humpty Dumpty 107 times isn't any adults idea or fun but they're only little once. It won't be long before they're too old to rock out to a bit of Humpty and you'll be nostalgically telling them about the tortuous hours and hours of nursery rhymes you had to endure because it was the only thing that made them happy.