Elliot and the goblin war maybe?
Or Goblins in the Castle? (There are two cover art versions in this Amazon link) https://www.amazon.com/Goblins-Castle-Minstrel-Bruce-Coville/dp/0671727117/ref=asc_df_0671727117/
I believe it's "Goblins in the Castle" by Bruce Coville. I loved this book as a kid.
> http://www.amazon.com/gp/product/0671727117
Holy shit! This is it! I recognize the cover! Thanks so much!
Goblins in the Castle. I'm being half-serious.