Hi everyone, I recently bought a mid 90's Fender Princeton Chorus and while it works like a charm, it does have some background noise which I would like to see gone.

When I disconnect the guitar cable i can crank the volume, both clean and overdrive and it'll give me very little noise, nothing to get concerned about.
Onc eI plug the cable in it gets hissy and it gets lous when I crank it, especially on overdrive.

What should I check to solve this problem?  Can it be a bad ground somewhere?
Is it dangerous to take the amp apart or is it safe as long as it's unplugged?

I'm not sure where to start here so any advice is welcome and appreciated.

Thanks!