Is a loose headphone jack causing poor sound quality?

Guffbox Asked: Is a loose headphone jack causing poor sound quality?

I recently have started learning to use Ableton Live Lite in earnest for some home recording. I am so far only routing my acoustic/electric guitar through Ch. 1 on the front panel of my TC Impact Twin Interface. I am monitoring live on a pair of Sennheiser HD 518s. I am getting a slight crackle in my recordings no matter how I tweak the settings. I switched headphone jacks from muting to non-muting, only to find that I was only hearing the stereo track of recorded audio out of the left channel on the headphones. When I pull the jack partly out, I can hear both channels, though the crackle is still there. Is it possible my headphone jack is damaged? If I don't touch the 1/4" pin, sometimes I get no sound at all. Is there any way I can remedy this?

Also, I don't quite understand what is causing the crackle. It seems to me that there is simply not enough headroom, so it may just be clipping (because it seems to only occur when the guitar is loudest). I don't know what to dial back to try and alleviate this. I have been messing with the "Adjust" knob for compression on that channel as well as the Gain Trim–and even some EQ built into my guitar. Here is a brief list of what I'm running, as well as the manual for my Impact Twin.

Any thoughts from someone knowledgeable about music tech?

http://www.sennheiserusa.com/audio-headp
http://www.tcelectronic.com/media/Impact
Guitar – Epiphone Performer ME