Evo n610c squealing when running off battery power

Im working on a Compaq n610c laptop. It runs fine off of AC power.
When I remove the AC cable there is a distinct squeal coming from the
computer. I have disassembled it and found that the squeal was coming
from the area of the DC-DC converter which is mounted right above the
processor. I replaced the DC-DC converter board, but the problem is
still there. To further describe this strange issue, when the battery
is in and the computer is not turned into the on position, there there
is a quieter high frequency clicking sound. When the power is turned
on there is a distinct squeal. Its not coming from any discernably
moving parts. Any help would be appreciated. Thanks!