[Mk2] [Generic] Stereo issues - speakers crackly

[mr2nut123]

So I had an old Panasonic CQ-VX5500K in my car and it was a double din unit so I wanted to change it to a single din player with MP3 and aux in.

I bought this ISO lead as I don't have the active system:

https://www.dynamicsounds.co.uk/autolea ... o-mr2.html

Since installing the headunit, my speakers have become crackly when I turn the volume up anything past 20. Up until this point, it's absolutely fine. Is this just a case that the stock speakers aren't very good, or would a bad earth do that?

Before I changed the unit, I noticed that the earth was clipped to one of the mounting screws on the side of bronze coloured mounting brackets to go into the dash. Should the earth go to a more ideal location..?