To objectively evaluate the background noise levels of vertical pendulum tiltmeters, we analyze tilt data recorded by six instruments installed at Hanzhong, Xi′an, and Qianling observatories in Shaanxi Province. Power spectral density probability density functions are employed to determine the background noise levels over the frequency range 10^-4-0.5Hz, and the corresponding noise sources are also examined. Our results show that: (1) The overall trend of background noise levels decreases nonlinearly with increasing frequency, with noise levels ranging from -43.5 to 43.5 dB. In general, the background noise levels at Hanzhong and Xi′an observatories are higher than those at Qianling. (2) In the 0.0001-0.0005Hz frequency band, the background noise levels at all three observatories are highest, primarily due to loading by low-frequency atmospheric pressure waves. In contrast, the frequency bands with the lowest noise levels for Hanzhong, Xi′an, and Qianling observatories are 0.02-0.08Hz, 0.02-0.04Hz, and 0.30-0.50Hz, respectively. (3) Double-frequency microseisms are recorded at all stations, while the noise intensity of ground microtremors at Qianling Observatory is relatively weak owing to the absorption and attenuation of high-frequency microvibrations by the loess strata. The results of this noise analysis are useful for characterizing the background noise levels of existing vertical pendulum observatories and for establishing noise models for the vertical pendulum network in China.