Hard to know if this is the best place to post this: Currently I am hearing what I think is clipping(?) in some song's vocals and instruments (like cymbal crashes) in my headphone setup. Bass response sounds fine but some high pitched sounds seem to distort pretty badly. I have a turntable -> phono stage -> WA6 -> HD650. I didn't notice this problem until recently; but, even more interesting is that it is only on some recordings (could it simply be the recordings themselves?). However, I think it might be due to the amp's tubes. One of the tubes was humming the other day and the tubes have been used a considerable amount over the last year. Could the tubes be a possible cause for what I am hearing? If it isn't the tubes then what part of my sound chain could be responsible? Thanks.
Here is a picture of the set up to make this post less of a bore: