I have an 86 camaro, 2.8 fuel injected v6. It has suddenly started to make a really loud high pitched noise. You can hear it through the heater vents. It seems to be coming from the driver side of the car. You can pinch the small vacuum line running to a box on the firewall and the noise will stop. I was told it was probably the egr valve or the heater control valve. Anyone got any ideas? Please