One speaker quieter than the other on laptop only

[harry97uk]

I have two JBL LSR305 speakers that have a TRS cable plugged into both of them that is then converted to a normal 3.5mm aux. If I play audio through my laptop, one of the speakers is quieter than the other. I switched the cables around to make sure it wasn't the speakers that were broke and the same thing happened but on the other speaker. So I assumed it was the cable that was the problem. I got a new TRS cable and the same thing is happening, however, if I plug my phone in then the problem is not there anymore. Why does this problem only occur on my laptop? Is there a problem with the input? I have a MacBook pro if that makes a difference

 

[ragnar-gd]

All audio connectors degrade over time, some oxidating, some "breaking" (not like "not working", but like "having bad contact after some time").
Oxidation can sometimes be helped with professional cleaning (ask in a shop), but for the degradation by wear and tear there is no solution.
How old is that machine?

 

[harry97uk]

All audio connectors degrade over time, some oxidating, some "breaking" (not like "not working", but like "having bad contact after some time").
Oxidation can sometimes be helped with professional cleaning (ask in a shop), but for the degradation by wear and tear there is no solution.
How old is that machine?

Early 2015 I think, thanks for the response