The new boards use 7mm PT screws (vice the 6mm PT screws that were used before).
As Chris P. suggests, if you have an older 6mm FS screw, it's a good idea to put some soap on it (as a lubricant) and screw it down straight in the FS screw holes (with out the
footstrap). This will tend to "tap" the correct pitch threads in the holes.
The use soap on the 7mm screws and they will go down in the holes pretty nicely.
The grinding noise you hear is the plastic trying to "stick" to the screw.
Use some soap to help with this and I think you will like the new 7 mm FS screws.
Hope this helps,