microphonic tubes

Hey guys,

I have a Boogie DC-3 and about a month ago the clean channel preamp tube (the original 12AX7) became microphonic. I replaced it with an EI 12AX7 and now it is also microphonic. So, I am wondering if some problem with the amp can cause tubes to become microphnic, or if it was just plain bad luck... Any input would be greatly appreciated. (Sorry if this is a dumb question...)

Thanks and my best to all,

Luis