Try Blu Tac on the 2 corners of the dust cover where it meets the base.
Rega TT Dust Cover Vibration
I have a P25 and recently while playing LPs loud (not ear busting, just loud enough) I discovered that the dust cover was vibrating quite a bit - enough to impact the playback. Anyone else have this issue? Short of taking the cover off, is there a way to defeat this gremlin??