I have an old bass that was handed down to me that I have been practising on, but I'm having some issues with the input jack on the bass. When I plug in the cable, it will buzz/scratch loudly unless I apply pressure to it, and then it's fine (it feels almost as if I can't plug it in all the way unless I push down on it hard). I've been using tape to keep it down in place, but it's getting kind of annoying (and quite ugly mind you). I've used two different cables with the same result, so it has to be the input jack and it's not the amp. Basically, what exactly is causing this? Do I need to replace the whole jack or is it something to do with the wiring? I'm not confident enough to open it up and fiddle around as I have no idea when it comes to things like this and don't want to wreak it further. Help would be much appreciated.