any slip yokes should have a grease fitting....
In your description of the problem you said it happens when you drive forwards and back wards and when you brake.
I'm assuming it pops when you take off frontwards or backwards but it only does it then and doesn't continually pop while driving???
I would suggest crawling under your truck again and get somebody to bounce your truck up and down while you lay under it and listen.
I don't think your Anti Rattle clip / Brake pad mounting clip will pop... especially while braking.
Let us know