Vacumn noise

[TMA62]

I just got my '71 Avanti II back from an off-frame mechanical restoration a couple of weeks ago and I am in the "shaking down" the car. One item that is to be addressed is a noise that sounds like a "horn". It comes from the engine and transmission area. It typically is not constant but I will hear it when I go over a bump or when there are there are passengers in the car in addition to the driver. In other words, it tends to occur when the frame/suspension is under a dynamic load. The sound will fluctuate a little in pitch and loudness when the car goes over bumps. Also, I will hear the sound when the accelerator is applied but the sound will disappear when I let off the accelerator.

We think it may be an improerly installed vacumn line. There are several vacumn lines for the engine so it may be a combination of them.

Have any of you encountered this problem and how did you fix it? Thanks in advance for any guidance or insight on ths matter.

[WayneC]

I would suspect the air cleaner... check to make sure there is a gasket between the air horn and the air cleaner, and that the air cleaner base is flat (no dings/distortions). And check the vacuum hose to the transmission.

[Tony S]

also check the pcv valve and the brake booster check valve that is right on the booster. Thet both have a tendency to make a noise akin to a kazoo sometimes.

[ernier]

I wouldn't think it was vacuum. Typically vacuum hiss would disappear as the accelerator is pushed since vacuum drops and increase when you come off the gas as vacuum is highest then the opposite of what you're experiencing.

I'm inclined to think the there is an exhaust pipe hitting and maybe causing a momentary leak when it does.

I'm having trouble with imagining a "horn" noise. Also, check any seals and body gaskets. If the shifter boot or seal around the brake booster and gas pedeal linkage is torn or loose you will hear lots of normal noises that sound abnormal because they don't normally get into the passenger compartment.