86' E28 535i Starter / flywheel problems HELP PLEASE

[palmerondrums]

so I have an 1986 535i e28 (automatic)
177k miles

I'm having trouble with starting the car SOMETIMES.
I have loud wrenching noise every once in a while (every 15 starts or so).
turns over and runs fine USUALLY, but every blue moon loud wrenching sound happens and doesn't crank.
Upon happening it drains my battery instantly, thus forcing me to jump car with cables (huge pain if i am out and it happens randomly)
thanks in advance! i need advice on how to go about this before i make purchases!

due to research i'm guessing it might be:

flywheel?
ring gear worn out?
starter?
Which parts should I buy for long lasting results since my e28 is my daily driver?


- Jordan

[BuzzBomb]

Have you solved this yet?
It's a contradiction. The loud wrenching sound that drains the battery. If it had anything to do with the flywheel/ring gear, it wouldn't start with a jump unless the flywheel moved to a good tooth. So I would rule out the flywheel. If it were the starter, I also don't see how jumping the battery would fix the problem for the moment. A ya gotta be kidding me possibility: One or both of the battery terminals have a bad connection to the battery. This would cause the occasional "dead battery" scenario, but actually the battery is fine, and the jump moves the terminals enough to make a good temporary connection. But this wouldn't explain the loud noise.
The fact that the jump starts the car is the part that stumps me. Also, nothing will drain a battery "instantly". That alone points to a bad connection, most likely at the battery. Still can't explain the noise though.