Loose or glazed fan belt. As soon as the battery recharges a little from the load of running the starter, the belt quits slipping. You're hearing the belt squeal as it slips on the crankshaft pulley as it tries to drive the generator or alternator under the load of recharging the battery. Tighten or replace the belt.
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!