Q: My car started making a rattling noise?

I spent a lot of time & money on my car in 2016 at a mechanic shop that was highly recommended to me in 2014 & where I had been going ever since it was recommended, BUT, unfortunately, this year I learned the hard way that it turns out that this shop is ran by a shady person, a slimeball mechanic. The knocking-type noise & the cooling system issue that I went in for in March 2016 was never resolved, after I paid for a ton of new parts; the noise has been there for at least a year now. The idler assembly had also fallen off my car while driving one night after that mechanic changed the belt on it. Then this past Tuesday a rattling noise began, it got louder & louder as the hours went on until it just stalled out on me, & it wouldn't start back up, & it still won't start. The key turns, all the lights come on, the radio & horn works, it just won't crank. I had also noticed an oil leak before this happened, and actually had just added a quart of oil on Tuesday before the rattling began.

My car has 257724 miles.
My car has an automatic transmission.