Turntable issue

You need to list your entire system and any changes. Make sure you didn't plug your phone pre into a phono input on your preamp.

Sounds like a ground has come off or broken somewhere.
Could be as easy as the ground from the tonearm to the
phono stage, or worse, a broken ground inside the arm-
tube.

It could maybe a bad tube in your Phono Box S or a tube
that is starting to go.

Also, you should always mute or turn the volume all the
way down before you do anything with a turntable.

You can do a simple trick:
use tape to attach any wire to the base of tonearm and connect it to the ground pin of your preamp.
If problem disappears, than ground wire is relatively easy to replace compared to the signal wires. The ground wire usually connects outside of the armtube, than goes through the hole and than out to preamp. The only trick is not to loose proper horizontal bearing tension if it needs to be removed.
If you want to communicate further, you can e-mail me.
I repair various turntables daily and restore them to original fully operational condition.

Thanks. I will try some of your suggestions. I was thinking it is a possible ground issue or a tube problem but wanted some others opinions. One of my tubes is looking rather black on the glass when I checked this morning. The other tube still clear. Sure would be easy if its a tube.

Only change I've made is running output to pc to transfer vinyl. Otherwise no other changes.problem wasn't there when I swapped output. Showed up later. Problem doesn't go away no matter the output either. I wouldn't think this has anything to with it.

before starting make sure your pre is not set to phono
1. check the ground wire, make sure its attached and not broken. usually you get very bad hum if its not connected but it can be lesser symptoms
2. check your cartridge leads to make sure they are tight. what you are describing sounds more like microphonic pickup from loose connection
3. if the RCA cables are user swappable, swap them and see if the problem goes away. if they aren't swappable make sure they are connecting tightly
4. possible that its a tube but microphony isn't a usual sign of tube aging... they get dull sounding. If you have connected a new piece of gear to your preamp, it may be causing you electrical problems. See if the problem goes away with only the Project Tube Box S connected as a pre input.