My GF's '96 EK Civic VTi makes an occassional high-pitched noise when the engine's running. Di siya nawawala pag pinapatay yung aircon. Sometimes meron, sometimes wala. Constant lang yung sound (same pitch even at high revs). Nawawala yung sound when I turn off the engine then turn it on again pero bumabalik din after around 2 mins.

Ano kaya problema?