Here is the deal with your preamp. And we retube them DAILY. The PV-10, 11, and 12 have a bit of gain and no feedback. They sound great, but if there is any pimple on the tube, you will hear it.
So the tubes have to be quiet. They also need to be tight and won't shake apart. If you have noise, there is noting you can do except put in the best tube. If you have microphony....the tube rings constantly and will not stop....you may want to consider, if it is out of warranty anyway, rubber mounting the transformer. I know guys that have done this and it helps. But it takes a bit of time as it is tight. The transformer vibration is picked up through the tube pins and slowly over a period of time it shakes loose internally.
If you want ease, find some RFT 12AU7. They seem to hold up. We don't sell them, as people look for something more "sexy". We use the Mullard CV4003. This is about the only tube that works well, and even at that only about 10% pass muster here to be used in those!