A rod knock or piston slap will change sound when the cylinder isn't firing. A main bearing knock stays pretty much the same, regardless of the cylinder firing or not. Main bearing knocks also show up on acceleration- - - - -a heavy BUMP-BUMP-BUMP-BUMP noise as the engine speed is increasing, followed by little or no noise at a steady speed.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!