You've isolated the problem as coming from the phono preamp or before. Good. Now isolate it further. Swap the L and R inputs from the tonearm to the phono stage.
Does the noise change sides?
If not, the problem's in the phono preamp. Check tubes and tube connections, etc.
If so, then the problem is one of:
- loose tonearm wire-to-phono cable connections or,
- loose cartridge clip connections or,
- the records are damaged or,
- your cartridge is mistracking.
My bet would be one of the latter two causes. If it happens on multiple records (or new ones), my bet would be insufficient antiskate force to maintaing stylus contact with the outer (R channel) groove wall. Try increasing antiskate a bit.
Does the noise change sides?
If not, the problem's in the phono preamp. Check tubes and tube connections, etc.
If so, then the problem is one of:
- loose tonearm wire-to-phono cable connections or,
- loose cartridge clip connections or,
- the records are damaged or,
- your cartridge is mistracking.
My bet would be one of the latter two causes. If it happens on multiple records (or new ones), my bet would be insufficient antiskate force to maintaing stylus contact with the outer (R channel) groove wall. Try increasing antiskate a bit.