[Help] Nasty (and loud) crackling noise from my dad's new bass

Does it make noise when you turn the pot back and forth?

 

Is it an active or passive bass? If passive, I would look for bad solder joints, or a bad capacitor. If active I would check the battery connection at the output jack, and if that's OK there's likely a fault in the preamp, which is not usually a DIY fix.

 

That's the classic symptoms of a dirty or worn out volume pot. Try cleaning the volume control first. You'll have to take off the back cover or pickguard to access the controls. Get the correct product to do this, just to make things extra confusing there's two companies that make pot cleaner with very similar names:
De-ox-ID and Caig deoxIT.
I don't think the brand is particularly important as long as you get "contact cleaner and lube" and not just contact cleaner. Pots have a thin film of grease inside to lubricate them so they operate smoothly and if you remove that grease with plain contact cleaner the volume control will wear out much faster.

 

It doesn't look like it's related to the volume pot. It makes noise while not touching to or moving anything. I think the preamp is faulty.
You should contact the seller and return the bass if it's possible. I don't think it's a simple grounding issue.