Problems with the noise floor and sensitivity can be due to factors like the mobile phase purity, poor analyte recovery, and various other factors. 

However, if the UV lamp is at fault, the phenomenon is usually gradual; the baseline will slowly becomes more noisy and/or the peak sensitivity will slowly attenuate. If this is the case, the lamp can be easily accessed from the detector module and replaced. To extend the life of your lamp, be sure to turn it off when the instrument is not in use.