Xbox 360, 3 red rings all of a sudden, power supply making a lot of noise?

Well sounds like you xbox **** the bed. I imagine that your xbox is a falcon or a the other chipsset prone to RROD. You could try to replace the x clamps but I wouldn't bother because you already have a slim. If you do want to replace them there lots of video tutorials on YouTube. Your best bet is to trash it.