CiG
Approximately Infinite Universe
There were earlier bands with a distorted sound, blue cheer had aggressive drumming which is pretty proto-metal but the rest of the band are just doing weaksauce chuck berry tribute, change out the drums and what do you have, it's wimpier than chuck berry actually. Helter skelter has a groove which is the basis of the headbanging riff and the song structure has peaks and troughs, it builds into breakdowns and acutally has groove. Find me something earlier that isn't just bad blues with distortion and aggressive drumming and I'll change my mind. You could say purple haze or something but that's as farty blues rock as it gets. Helter Skelter is when it actually got heavy.
Actually listen to the groove and the dums.
The entire Deep Purple debut establishes heavy metal without relying on merely distorting blues rock, and in particular "Mandrake Root" hits all the marks for headbanging, grooves etc.
Then you have Steppenwolf's single "Born to Be Wild" which is pretty god damn indicative of what would become typical heavy metal, especially with its repetitive use of a distorted riff.
But all this is irrelevant because Blue Cheer recorded shit like that in 1967, and as much as I love that Beatles track/album they were well over a year late to this discussion.