You need to narrow it down. All analogues to all digitals? Or just a specific SLMA/SLMO. And if it's just a specific card, is it the only circuit on that card, or all circuits? Can you get it always from the same analogue, or always the same digital? etc etc. You need to test.
If the 4K is a duplex processor you might try reloading the standby processor, then switched the active processor over to the standby. But if there are no hista messages, it could just be your phone hardware.