Dennis,
One of the first models I built with electric had a 3-ply exterior grade 1/8” plywood front mount that always gave me fits and it acted like it was loose (it was). I fixed it by installing eyelets on the back side (inside the front mount) then trimmed the eyelets flush withe the front of the mount, this kept the bolts from crushing the plywood mount when the bolts were tightened up. It worked pretty good but I don’t use plywood for the front mount for that reason. Use 090 Circuit board or G-10 is the best I’ve found so far.
Later,
Mikey