Remove the Frame. Plug in and check what you're getting on the LEDs.
Diagnostic LEDs are to the right of the RAM slots (this may be covered by a piece of black electrical tape extending up from the bottom edge of the logic board). Ple4ase let us know your results before buying anything as #1 should be on even if the power supply is bad. See if you can discern where the noise is coming from.
LED Startup Sequence
LED #1 = Power available.
If no LED is visible:
• Verify AC source
• Verify known-good AC cable is connected
• Verify cable connection between AC inlet and power supply
• Verify cable connection between power supply and logic board
• Verify power supply
LED #1 + LED #2 = Power available, and system is powered on.
If second LED is not visible when power button is pressed:
• Verify power button connection to logic board
• Verify power button functionality
• Verify cable connection between power supply and logic board
• Verify power supply
• Verify logic board
LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.
If third LED is not visible after power on:
• Verify that MXM video card is seated properly
• Verify logic board