Well, the problem is very simple, anybody who knows the A-B-C's of plumbing could have figured this one out.
A scientific explanation for this obvious case of haunting? Really?
I found evidence that some emergency repairs were made to the central system manifolds. It seems that a high-pressure gas line was mistakenly hooked up to the fluid lines.Any time the plumbing cycles fluid, that gas rushes through the system, and it sounds like a voice.
Ghost In the Pipes:
YOU ARE ALL DOOMED
See? It's just bubbling noises. Not a voice at all.
'D' is for 'Denial.'