Weird Noise

If you can, get it on a hoist. "I'm normally alone" so I do crap like tie a scrap of wire to the throttle, run clip leads down and hang below to control ignition and jumper starter relay, and get under there an poke around

Use a piece of hose---almost anything---heater hose fuel hose, etc, as a stethoscope to your ear.

Pull the belts all off and run it a short time with them off FIRST

Suspect and check EVERYTHING

Exhaust rattling......already mentioned

Broken / weak motor mount or even missing support bolts

Loose/ bend / improper converter dust cover, even bell loose to engine

Inspect carefully....."its been known" LOL to dent the pan and rub the crank

These are just a few. SUSPECT.........and CHECK

If you suspect valve gear, LISTEN with your hose device........stick the hose into the oil filler, onto / into the PCV grommet, etc. Don't wast time........if you "think" you hear it "up there" yank those valve covers!!!!