Separate noise (a fast, jagged baseline) from drift (a slow climb or fall). On a UV detector, common routine causes are an aging lamp, a dirty flow cell, bubbles, or pump pulsation. On either HPLC or GC, a contaminated column or a bad mobile phase or gas can look similar.
For HPLC, degas the mobile phase and purge the pump. Confirm the lamp is on and note whether noise grew worse as lamp hours rose. A bubble will often spike and then recover; a dying lamp usually does not.
Do not open a flow cell or a detector that is not designed for user cleaning. Call Mahut if noise remains after degassing and a simple lamp-energy check, or if the detector will not ready.