Xbox 360 power brick problem

This may sound like teaching you to suck eggs, nut have you checked that all the connections are good, i.e. plug to power brick and power brick to console? When I fist got my new 360S I had a power brick problem like the one you are having and it turned
out the cable from the mains to the brick wasn't pushed in all the way. Short of that all I can suggest is this link to the Xbox support page for power problems.
Hope it helps!

That sounds... odd. The power brick doesn't have an on/off switch and the console's "switch" is really just a power switch relay like a PCs, not an actual power on/off switch.

The power brick isn't user servicable, like most PC power supplies. I assume you've tried swapping power bricks with a working console to see if the problem is the brick or the console?

There's also the
power supply troubleshooter.

Unfortunately, no. My sister is borrowing her boyfriend's xbox 360, but it's the older model, not the slim, so the connection for the power brick is different.

But yeah, I think I'm going to go ahead and get a replacement brick. As I said, it makes a very audible noise, which it probably shouldnt be making, and there doesnt seem to be anything wrong with the console itself.

It could be heat with your console. Your PSU doesn't make any noise, or--it shouldn't. It has no moving parts. The only moving parts are the fan in your console and your DVD drive...and to a lesser extent your HDD. In any case use a can of compressed air
to blow out the vents at the back and sides of your console, top and bottom, and then do the same to your power supply. _DO NOT_ use a vacuum cleaner or any electric machinery to blow the air out. You can get a can of compressed air for a couple of dollars.
Your PSU appears to be fine, so it's probably your console.

It turns green when trying to power on, then quickly reverts to orange when it fails to do so.