Popping Noise when I put my foot on the brake in reverse

When I am backing up and I put my foot on the brake I get a popping noise coming from the right front tire area. I can also feel it in the body of the car, its like something is loose. It only does it when going in reverse, going forward and putting my foot on the brake pedal is fine.

I thought it was the break caliper being loose, but all the bolts are tight. It is not the ties rods as I put new inner and outers on two months ago. Anyone have an ideas what I could check?

Thanks

Greg