Fast, regular ripple often comes from air in the pump head or a check valve that is not seating. Slower wander often comes from a small leak, a partially blocked inlet frit that starves the pump, poor degassing, or a change in temperature or solvent composition.
Purge each channel in use. Confirm the inlet frit is not blocked and the bottle is not empty. Watch one channel at a time if you use a gradient. If a single check valve or seal has just been disturbed, air is the first thing to remove before you replace more parts.
Call Mahut if purging does not settle the pressure, or if the ripple started right after a seal or valve change and priming does not clear it.