Earlier this week I fought with it not wanting to start, after changing the fuel filter. The battery had gone dead from trying to start it over and over again without success. After I cleared the problem, and had it jumped, it ran perfectly fine. Also let it run a while to recharge battery sufficiently.

Now a few hours later, it will not start once again. Would this just be the battery working on it's last days, or is there something causing the battery to drain by itself while the car is off?

Also this time around, when I tried starting it, it made a different kind of noise than normal. It's hard to describe, but it sounded almost gritty. Like the parts moving around are coated in sand. It sounds weird, I know, but I know for sure it doesn't sound like it should.

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1981 300SD, odometer stopped at 188,000