clunking or popping sound when i brake when wet outside.

i'm getting a popping or clunking sound under my car when i brake. it only happens when it's wet outside. i just took the car to my mechanic because
i had the left rear shock bolts break off from being so rusted out. they
drilled out new holes and bolted it back to the undercarriage. i wasn't
getting the popping/clunking sound before they did this. at the same time
i also had the car inspected. the shock does look very rusty but they said it's working fine. not so sure though. i was thinking maybe they didn't tighten the brakes right when they inspected them. any help with this problem would be greatly appreciated.