I have recently bought a Fender Hot Rod Deluxe II. When I got it sounded a little muddy, and the first preamp tube seemed to be microphonic, so I bought a replacement 12ax7. Except that a couple of days into playing, and it seems that this tube has now also gone microphonic. It is in the v1 position. Any help would be greatly appreciated, or any advice on what the potential problem could be. Thanks!