Just a simple online search of the term "metal band" should bring up links to many existing or past bands. Model yours after popular groups such as Black Sabbath, Rotting Goat, Judas Priest, Slipknot or Leper Zoo. Names often result from combining two ominous words that aren't necessarily grouped together in everyday conversation (ex: Cannibal Corpse). Make a list of possible names and vote with your band members on the best ones. Try to give them a personal flair that doesn't deviate too much from popular bands.
There are many so-called "name generators" that randomly combine words together from an appropriate word bank to create metal band names and the like. The website Metal Band Generator is a free platform that creates metal band names for no cost. Simply click on the "generate more" button to see a list of 10 possible names. Testimonials on the sight attest to its success.
Maybe you're in a metal band that plays covers or is particularly inspired by a certain group. Try aping their name with something similar (but slightly different) that plays off the popularity and image of the existing band. For example: "Degameth" for those who enjoy Megadeth or "Metarrdica" for fans of the band Metallica.
First you'll need to decide what your group is about and what image you'd like to promote. If you enjoy thrash metal and playing at fast speeds, you might opt for something like "Thrash Babies" or "Speed Freeks" (misspelling common words is popular in this genre). Try incorporating popular actors or politicians that you like (or dislike) into the name, for example: "The Keanu Reivers of Death" or "Sarah Palin Impalers."