Double bass strings

Technicality

I have been given a very old double bass by someone who is leaving the country.

Only problem is that the middle two of the four strings (A and D) sound rattly and awful. After failing to locate the problem on any part of the instrument (loose bits etc) I got someone I know to try out those two strings on another double bass and he said they sound similarly bad on that one too. I guess this means I need new strings. Should I replace the set or just replace the bad strings? The ones on there are metal.

I play bass guitar, but I've never played double bass before so I have no idea what I'm looking for. I'm mainly wanting to just have a bit of fun with it now and then so I'd prefer not to spend too much money.

I guess I am looking for something that is a value for money not bad all rounder I can try things out on. I don't really know how to proceed from there though (googling has led into pages and pages of discussion on the latest greatest and not much else), does anyone have any advice?

Pheezer

I'd take it to a shop that rents double basses and see what it'd cost for a string replacement/setup. You might get the tech to walk you through how to do it in the future.