Could you help solve this lawnmower mystery?

How old is the gas? you may have to drain the tank and put fresh gas in to get it to run.

@WestRiverrat Would that account for the noise, though?

Is the clattering/squealing a sticking clutch? It might not idle well at all if the idle clutch is bearing when it shouldn’t.

Old gasoline equal NO START. Drain fuel and get some new fuel, gas can have fuel from last year? Use stabilizer if you put the mower away for more than three month. The gas-a-hol soaks up water and also cause gum in the fuel line.

Is the squeal from the belt? Does the blade have a safety lock on it – like a chain saw kickback brake? The brake can be on, with the blade release mechanism hung up so the engine starts, spins for a second and then dies, squealing until the engine stops.

I thought more about this. Look at the blade brake clutch. I’m guessing it, or the cable to it, is seized.
Take the belt off if you can and see if the engine runs well. That would isolate the problem.

Turns out the throttle was too far over. Thanks all!