keyon, very bad, and cranking very common.
battery power is weak, not 12.6v rested.
use a volt meter
or jumper cable start it.
walfart has voltmeter for $10 , the $20 Crown VIc meter ,is 20
get a cheap DMM and see.
or here.
a whopping 15 bucks and magic happens, you see the system mess up even driving. same place next o car batteries, walk in. see it.
http://www.walmart.com/ip/Equus-Innova-3721-Battery-and-Charging-System-Monitor/15137663
if the battery is good and the meter above is low, the cars wiring is bad. (corrosion does kill all old cars. )
i restore old cars, and can show this all day,..... its endless.
have lots of photos too.
that clattering is all the computers in car, (1 or 2 back when)
are going NUTS with 1/2 power appied. all modern cars do this.
and worse newer, (be happy car is not new)
Sig: I must ask questions first, I'm blind, and my tools can't reach, dig?