Audio Output Distortion on 3.5mm Headphone Jack

I've been using the machine everyday for many many years, especially for audio. One day I had the 3.5mm output plugged into a synthesizer to filter and mod the sound and some how some DC voltage leaked back into the mac and ever since then the port works, its just super noisy/distorted Whats even weirder is that the I get weird grounding noises/issues when I hook the mac DVI up to an external monitor. It gets amplified when I plug in the mag safe charger. These noises/issues can be heard thru the audio, even slightly when using a usb audio interface. Fortunately I have a parts unit to pull from. Has anyone seen this before? My first guess is to swap out the audio in/out board, but beyond that I dunno. If there are any board level repair guys who can give me advice. Thanks!

So I did it and right when I got the audio board out I notice a blackened area, sure enough it toasted some resistors/caps, replaced the board and its all good! Thanks