I agree with trying to adjust the receiver in the bumper.

When we bought our '08 XC70 used car, there was a rattle in the rear, I thought it was in the rear suspension, but this receiver needed adjustment.

4 years later it is still fine, but the tailgate handle does not always work when I unlock it - I just have to flip it a bit in the wrong direction, then it works fine.

The tailgate latch is controlled by rods and plastic bits that keep the rods in place. It is a pain to remove and replace, but can be done. When the plastic bits break, you are probably out of luck.

When you use a screwdriver to 'latch' the lock, did you go to the second click or just the first?

Make sure the receiver on top of the bumper is clean of dirt/sand. Close the tailgate slowly and listen for 2 clicks. If you only hear one, and pushing on the tailgate doesn't add a click, adjust the bar on the bumper using a T40. Adjust 1/16 of an inch at a time.

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Keeping it running is better than buying new