Weird audio port issues

I've had problems in the past with needing to wiggle and twist my headphone jack into the right place to get a full sound, but recently I haven't been able to do this. I discovered that if I go into the audio output settings and change the balance to far left or far right, the sound comes out full and clear in mono. Only when the balance is at or near the middle do I get what sounds like a 'noise cancelation' effect where certain frequencies are muffled and it sounds like theres a spectral gate on the output, kind of like when headphones are half plugged in. I've tried cleaning out my port. Any suggestions? Thanks.

Sounds like one side or the other is maybe out of phase, although I have no idea how that could happen.

You could try using a vacuum cleaner to clean out the port. Always vacuum, never pressure. You could also use electrical contact cleaner on a cotton bud for a more thorough cleaning. I have to admit I don't like the idea of ramming cotton buds into computer equipment, but opinions differ.

I assume you've tried multiple sets of headphones to isolate the root of the problem?

If the headphone jack is toast, there are a couple things you can do to get around it. Use the optical output. Plug a miniTosLink cable into the headphone socket and the other end into an amplifier. Or use AirPlay to direct the output to an AirPort Express and plug your headphones into that.

You could also check the port itself with a 3.5mm stereo cable terminated at the other end with stereo RCAs and plug them into an amplifier.

BTW, I'm dead serious about the vacuum cleaner. It works a treat on sticky iPad headphone sockets. Get as good a seal as you can, but no need to break out the duct tape.