Pull spark plug wires off the plugs (with some well-insulated pliers) one at a time to see if you can isolate which cylinder has the problem. When the plug quits firing on that cylinder, the noise will either go away or at least change sound. It sounds like you might have a sticky intake valve. Sometimes drizzling a lightweight tuneup oil like Marvel Mystery Oil down the carb throat with the engine running at a fast idle helps, but be aware that you'll create a cloud of blue smoke that will put a mosquito fogger to shame! If you've got snowflake neighbors with lace on their drawers you might get a visit from the fire department or the clean air cops from CARB!
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!