Replying to Noise Reduction with On-Board Recorder (Tascam DR-40)

Just got a 2.5 to 3.5 cable and hooked up my GH2 to my Tascam to use the Tascam as an on-board recorder, however, I've been running some tests and have been getting some pretty obnoxious static noise in the background. I turned off everything in my room so it was absolute silence and reduced the Tascam settings to -12 db (lowest) and the GH2 to level 1 (lowest), unfortunately the noise is still there albeit somewhat stunted.

The only thing I can think of causing this noise is that the headphone/line out from the Tascam is over-charged when going into the GH2's mic input as headphones are usually a higher level (don't know the unit, db?) than microphones and the Tascam's line out is intended to be a headphone jack.

I'm not too sure how to remedy this issue and it's tough to find information pertaining to recorders so I'm wondering if anybody on here can let me know what i need to do, any help is appreciated. Thanks in advance guys. Sorry for the rough explanation.