Childrens/ YA Fantasy. Haunted mausoleum in a graveyard with a singing, narrator, pirate rat.

[Hadassah 💙]

i read this book in upper elementary school, around 2008-2011, and i dont believe it was very old at the time, so maybe published late 90s-early 2000s. i remember the cover being a giant stone mausoleum that your made to be looking up at during a lightning storm. i honestly dont remember the main character, i think it was a young boy, but basically hes exploring around an old abandoned mausoleum that has mysteries and a treasure chest and stuff inside it. the main thing i remember is there was a rat living i side who was a sort of guardian that is loosely narrating, but he repeatedly sang (maybe about a dozen times), “drink up me hearties yo ho” and “yo ho ho and a bottle of rum.” i remember the name being very simple, like literally just ‘mausoleum,’ but i cant find anything by that specific title, so its gotta be something similar. thanks!

[Ayshe]

The Mausoleum Tapes maybe?

[Kat]

I don't know if the singing rat fits, but maybe The Graveyard Book?
Check out this book on Goodreads: The Graveyard Book https://www.goodreads.com/book/show/2...