MacBook is suddenly very slow to respond

My MacBook started to suffer from the issue of being stuck on Optical Audio Out unless something was plugged into the audio jack. I tried to fix that issue by doing an SMC and PRAM reset and after the reset booting/click response/shutting down, basically any action that I took would take about 20 seconds to see a response. I would just get the pinwheel.

I took it in to Apple and they looked at it for 2.5 hours. Mostly tried to reinstall the OS, but they couldn't format the SSD. It would just fail any time they tried. It also couldn't complete a disk repair. They decided it was probably the hard drive.

I went and bought another hard drive and I couldn't format that either. Then I tried putting the old SSD in an enclosure and booting from that. Everything seems to work fine!

Does that sound like it is just the SATA cable? Is it likely that replacing that would fix the problem I am experiencing?