2001 Suzuki Grand Vitara - Front CV Axle

Okay, so I recently got a used grand vitara and the cv axles seem to be on the way out. I noticed the boots were torn, but they weren't knocking when I bought it. I threw it in 4wd the other day and noticed that they do knock when the vehicle is in 4wd now (suzuki is rwd, it's the front shafts in question)! So here I am, wondering how soon I need to replace these. Could it still fail drastically if there's no binding sound in 2 wheel? Money's a bit tight right now, but I also do not want to risk that failure. Thoughts?

Also, if anyone has done this vehicle and has input that'd be great. Haven't been able to find a tutorial yet.