[fahadkhan]

Audio quality on my headphones (Senheiser M2) is better via Bluetooth than wired. Not sure why.

[varjag]

The built in DAC/amp on 'heiser is likely better than the piece of crap serving the 3.5mm jack in your phone.

[fooker]

Faulty wire

[fahadkhan]

Didn't think of that, haven't tested it but strongly doubt it. I'd expect a faulty wire to crackle predictably when moved which isn't what I experience.

[fooker]

There can be many kinds of faulty. Some faulty wires crackle when there is something broken that comes into (and goes out of) contact when moved.

For example, having uneven thickness will noticeably reduce audio quality like you mention.