Put your old coil stops back in and see if it goes away.

Modern Coil stops don't work well on EMs. You need the older style dual metal stops so they don't get magnetized.

If you old ones are really worn you can swap out some from less used coils like the credit wheel or other mech like that. Put the new ones in those assemblies.

Also ensure that you squeeze the coil stop when tight it down.
https://pinside.com/pinball/forum/topic/vids-guide-to-upgradingrebuilding-flippers#post-284670

Make sure the EOS switches are adjusted properly.

Whilst you're in there I would rotate the coils to keep the lugs away from the stop.

What's it sound like when it's down & glass on?

They seem okay, nice spark coming off of them so looks like they are opening fine.

Can someone who really knows about this weigh in? Is it normal for EM flippers to be this noisy? I have read in a different thread that you need to align the coil stop to be square to the plunger, but I have no idea how you would accomplish that.

Your return springs might be too strong.

nice one! To test that, push/compress the spring to reduce tension when the thing is buzzing ... or remove the spring (and always play the game with the playfield vertical )

for coil stop alignment, you can loosen the coil stop so it can shift around a little and see if it still buzzes when loose.

the brown plunger link doesn't hit the end of the coil sleeve, does it? Sometimes you need to trim the coil sleeve to shorten it a bit otherwise the plunger is held up off the stop.

the bouncy issue is usually the EOS switch isn't closing soon enough. When a ball hits the held-up flipper, the flipper deflects down enough to open the EOS and re-energize the high power coil, causing the flipper to flip again. Make the EOS close a little sooner in the plunger travel.

Did you flipper rebuild kit come with the correct coil stops for an em? The correct coil stop for AC flippers is A-613-67.