So i got a double din installed on my car and after about a month my system would just randomly turn off(headunit would power off and same with subs and amp) it did it once then would reboot. I took it in they changed the wire harness and the ground. It fixed it for about 2 days i then decided to change my negative battery cable and that fixed it for a few months and then it came back and i noticed that with the head unit turned off that there was a bass note from the subs playing real faint until i turn the bass knob it gets louder. What could be the issue on why my head unit turns off by its self faulty head unit, bad amp need help asap.

I'd recheck your wiring.  Sounds like your "fixes" jostled something that actually did the fixing.

I had it all done at a shop they tried fixing it by first replacing the harness then moving the head unit ground to the ignition that didnt fix it but when i changed my neg. Battery cable in the engine bay it fixed it for a while i have a feeling its the head unit because i had the rest of the system hooked up before hand and didnt have any issues with the stereo doing that with the stock unit