Hi SJWorne,
I tried the same Valvo 6CQ6, and found them to be very microphonic indeed, though quite good sounding after a period of burn-in. I replaced them with the Mullard M8161 (CV4015) which are not at all microphonic. I can tap them and hear nothing through my headphones. They are mil-spec, so probably have more robust innards, less prone to vibration. Additionally, the Mullards sound quite a bit more refined in every way than the Valvo 'equivalent'. Like all Mullards, the M8161 is on the warm side, but in a very likeable way, if warm is your taste.