Today I ran into some issues with my brand new 20w s1.  My first few days with the machine have been great, cutting and and engraving have gone perfectly.  I started off with plywood then spent the last few days doing slate coasters.  I went back to ply wood today and found the  engraving wasn't as clean as it has been, almost like the air assist wasn't working.  I do have air coming out but noticed the air assist makes a loud buzzing noise the higher it goes, not sure if that's normal?  Also at 100 power and 10 speed, its not even coming close to cutting out 6mm ply.  I was able to do this initially no problem.  I took the laser apart for cleaning but I don't see any visible dirt or debris in or around the lens.  Any thoughts would be greatly appreciated.