Sounds a lot like a tube to me. Easiest way to check is to simply swap the present tubes, in pairs (though I assume there'll only be one pair on the phono stage...?), between the two channels. If the noise moves between the channels with the tube, then there's your culprit. Most tubes will have some level of "tube rush" (much like the pink noise your talking about). But if it's loud enough to bother you, then it's definitely not one you want to keep.
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