MBP Reporting HDD Space wrong (Missing 130GB and counting)

I apologize for being dismissive towards the helpful amateurs, but Ive got a problem that goes beyond the basics. This is NOT a case of emptying the trash or understanding binary reporting of HDD capacity. So I need help from people who know what they're doing.

System: MacBook Pro 15 (Early09). 500GB 7200rpm. 4GB RAM.

Problem: OSX mysteriously eating away at free space in realtime. So essentially I've got a 364GB of actual used but instead of reporting 130GB free it eats away at free space until it hits Zero free.

Timeline: The issue is relatively new. I suspected improper reporting of free space but for the last 3mo I've had 70GB open so I didnt worry. But today I received a notice stating "Low Disk Space" and watched as it literally dropped from 10GB to Zero. I deleted 20GB of files only to return later with the new freespace devoured again. NO new software was installed

Solution Attempts:
- Internet. Several similar reports, zero reported solutions
- Software. Disk InventoryX, WhatSize, Grand Perspective. These all report USED space but my issue is they add up the proper 364GB used but don't acknowledge or display the missing 130GB.
- Permission Repair through Disk Utility from Boot Disk and within OS
- File deletion. Any free space is gobbled up by this mysterious problem resulting in NO free space.



So there you have it. I'm adding up 364GB used space but the computer is claiming 479 and would take more if I had it. So... Any guesses because I need to get back to work.

 

Nailed it. Time machine created a Time 1 disk that i guess was hidden on the primary drive and I also found a 2nd Mac drive listed there. I was actually only expecting 60GB back since thats all I had free before i noticed this problem but I deleted them and got 110GB back. Thanks so much!