plim22

I just got my front brakes replaced and rotors machined. When I drove off, I noticed it making a knocking sound when I stepped on the breaks and start to slow. It only happens when braking, almost like ABS sounds but much louder and happens always when braking. I took it back and they told me it was my wheel bearings... but it's strange because wouldn't it make the sound all the time then? I need to drive 6 hours next week and need to get this fixed, but I don't wanna get ripped off either, so I'm trying to figure this out first. Please help!