Noisy Logic Board, PB G4 17"

[toygasm4u]

Hello All. For some time now, I've noticed a bizarre "squeel" coming from the bowels of my powerbook under certain circumstances. 75% of the time, when I hear this noise, it ends with the PB locking up.

Circumstances include: FW400 drive plugged in, USB flash drive plugged in, PCMCIA SD reader plugged in.

Long story short, when I have an accessory / storage device plugged in, this PB squeels like a stuck pig.

Where is the sound NOT coming from? Speakers, Optical Drive, cooling fans, hard drive. These things have been ruled out. The noise is coming from right in the middle of the keyboard. As I said before, when I'm transferring pictures off an SD card, or doing a large file transfer from the FW drive, my PB has a real hard time keeping it's composure, and I'll quite often get the spinning beach ball. This usually results in me hard-booting the machine.

Attempts made so far:

PRAM reset, Power controller reset, Reinstalled OS-X, repaired permissions on the disk via target disk mode.

Is this something going south on the system bus or something? Anybody experience this before?