Please let us know where this ends up...people won't continually make fun of you...a week or two at most...maybe a resurrection in a few months.
Also, so you know where you stand...you did not shift from 5 to 1st in a manual...still trying to figure that one out...and you did not connect battery in reverse...nor did you ignite yourself on fire so your son could produce a cool skateboarding video!
But, first, don't do that again...and second...don't listen to those who say don't worry at all about it. If you think you should worry about it, then do so until you understand what happened. You described something that sounded like an issue and happened just after this shifting snafu...so study up a bit on it.
Also, if it was me, I'd study up on changing trans fluid...and if this sound is a bad sound, and continues, then I'd find out more about it. See if someone can start car while you listen with hose to isolate it. If it's in the trans, I know that's not good news, but it's better to know now while there's a shot a simple intervention, rather than wait until, say, a stray tooth from a gear, say, chews other pieces up. I'm not saying that's what you did...but saying don't just hope nothing bad happened...figure out what did happen and then go from there.
You have a great advantage in figuring things out...you know what you did.
I'm not disagreeing with those who say you did nothing, as much as agreeing with you, thinking you did something!
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Mangofy your E46!