Hi, recently hooked up a optoma hd180 which is very similar to the hd20. However while watching a movie etc... i nptice there are white specks all over the screen and they kind of flash, kind of moves too. Its all over what can be wrong?

Hey everyone, Recently got Optoma HD180 (haven't received yet) and looking for a Diy Screen paint. 1. Screen will be approx size of 4ft by 8ft 2. Not sure what substrate to use so any ideas for something cheap would be greatly appreciated (though leaning toward thrifty white hardboard...