Attack of the Graveyard Ghouls (Goosebumps Series 2000 #11) by R.L. Stine

Dead but not buried...

The fog shimmered up over the dark grass, over the bent, scraggly trees. Covering the hill, covering the old graveyard.

Spencer Levy heard the horrifying moan. Though the windowpane, he heard a long, low moan floating from the hill.

Human and animal at the same time.

So cold. So sad. So near...