brakes grinding why?

I recently had my brakes replaced at 60K miles (rotors, drums, non-organic pads and shoes) and now experience a slight grinding noise when pressing hard on the pedal. The breaking isn't affected as the car stops fine. The noise and feel of the pedal sounds as if the pads or shoes are chattering, but upon inspection by a qualified mechanic, he didn't find any issues and stated to switch to organic pads, which he said are softer and should eliminate the noise. Why would this matter? I paid for the higher quality pads, but the hardness is what the mechanic is saying is causing the grinding sound.

Only other work done to the suspension is new struts all around and new tires same time as break job . I also had an alignment done with the new tires and had the suspension checked for problems and none were found. I had the mechanic check the front wheel bearings and control arms and joints and no signs of wear or damage.

Depressing the break pedal slightly causes no grinding sound, only when pressing it medium to hard and when the noise is present, the pedal seems to vibrate slightly or I feel the grind through the pedal. I had the front rotors checked for any warpping and they tested true, so this problem seems perplexing. I don't want to replace pads as I'm going to incur a cost and it may not solve the problem. On a limited budget and after having paid for a full brake job, I'm a little leery about going with cheaper pads to stop the noise.