general brake pad problem

[gra]

hello all just a quick generalised brake pad question this is not on my falcon but a express van
replaced brake pads the other day all went well used the 4wd/pro ones from repco installed ok drove down freeway for 80km ok
after about 2 hours driving there is a noise that seems to change from hardly noticeable to sounding like the wheels are about to explode or implode its a metalic noise that as i said sometimes gets real bad sounds similar to the tags that some pads have but is not always present i was thinking maybe the shims that came with them so was wondering as the fords ive replaced dont recall them having shims if maybe they had come loose and if so would it be ok to just remove them ?
the brakes are working very well when i apply the brakes in fact very impressed with how well they are biting in when i press down on the pedal

thanking you in advance for any advice
cheers