So, months ago my rear brakes started squeaking only when i Reversing, I went to a mechanic and he told me we needed to change the pads. But after some km they started squeaking again (only when i Reverse), what could be causing this? 

Car is Ford Focus 2005 Mk2

Are the pads chamfered on each side?  Cheap pads tend to be totally flat across the face.  The sharp edge angle created at the front will cause a squeak when reversing.

10 hours ago, TomsFocus said:

Are the pads chamfered on each side?  Cheap pads tend to be totally flat across the face.  The sharp edge angle created at the front will cause a squeak when reversing.

Not only do they squeak when I reverse, but you can also hear it sometimes on some turns or when I accelerate forward slightly/slowly

1 hour ago, ard98 said:

Not only do they squeak when I reverse, but you can also hear it sometimes on some turns or when I accelerate forward slightly/slowly

Sounds like the pads are loose in the carrier.  There should be a spring or an adhesive backing on the pad to stop them moving.

Ultimately you're going to have to remove the pads again.  Check why they are loose.  And also grease up the slide pins with red rubber grease.

9 hours ago, TomsFocus said:

Sounds like the pads are loose in the carrier.  There should be a spring or an adhesive backing on the pad to stop them moving.

Ultimately you're going to have to remove the pads again.  Check why they are loose.  And also grease up the slide pins with red rubber grease.

Thank you! I'll try that