High Pitch Noise near firewall

[00-711]

Hello,
           I've started to get a high pitch noise after I've been driving awhile. It sounds like air coming out of a small opening. The pitch of the noise rises and falls as I depress and let off the gas. The noise will go away if the car idles. Sounds like its coming from inside the engine compartment near the firewall in front of the steering wheel. It's been doing this for over a year. No real other issues except the noise is annoying! It's very bad when driving on the highway.

Thanks,
00-711

[carnuck]

Or the lines running behind the head to the tcase? Mine were cracked there. Bad brake booster could do it too. Pull the hoses off one at a time and see if the noise goes away.

[BenM]

There's both the 4wd switch and the heater unit under the dash that have vacuum lines. Plus if you've had backfires they tend to pop the vacuum lines off of the accessory fitting at the back of the intake manifold, and that is just on the other side of the firewall from the driver. It can be quite noticeable.