This paper presents an investigation into the characteristics and contributors of a friction-induced squeak between head restraint fabric and rear glass in small trucks. The in-vehicle vibration is simulated by introducing relative motion between the fabric and glass in a controlled environment. The influences of fabric material, foam material, temperature and relative humidity are studied while varying the frequency and amplitude of the sinusoidal input. The Taguchi Orthogonal Arrays technique is utilized in the design of experiments. Simultaneous time-frequency plane Short Time Fourier Transform (STFT) technique is combined with variable digital signal filtering to evaluate the squeak pattern. Loudness levels of the sound signals are calculated and are used in the Analysis Of Variance (ANOVA). From the results of ANOVA and squeak pattern analysis, the humidity is found to have the biggest influence on the squeak and the foam material is found to provide the system flexibility necessary for the squeak generation. From the time domain and the frequency domain analysis, the squeak is characterized as time varying periodical sound bursts, with four bursts in each reciprocating cycle. It is also found that the frequency content of the squeak consists of a time varying fundamental frequency and its harmonics.