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Just to confirm, this noise only happens when you shutoff the engine, does it happen immediately after cutting the engine or is there a delay?
My guess with the limited information and listening to the noise in your recording, is that this is intake/engine vacuum related. Possibly a failed or failing check valve for the brake booster, or a failing diaphragm in the brake booster. It could also be a cracked or leaking vacuum hose or connection. If you can reliably re-create this condition, I would pop the hood and do some basic sound checks to pinpoint the location of the noise and go from there.
-Icer
Just to confirm, this noise only happens when you shutoff the engine, does it happen immediately after cutting the engine or is there a delay?
My guess with the limited information and listening to the noise in your recording, is that this is intake/engine vacuum related. Possibly a failed or failing check valve for the brake booster, or a failing diaphragm in the brake booster. It could also be a cracked or leaking vacuum hose or connection. If you can reliably re-create this condition, I would pop the hood and do some basic sound checks to pinpoint the location of the noise and go from there.
-Icer
It’s a 2004 Enthusiast with a JATCO RE5R05A 5-speed transmission. Theres about a 3-10 second delay after cranking the car completely off.
I could be wrong, but my hunch/gut is telling me this is vacuum related. It could be something else, but with a 3-10 second delay, the only other components I can think of that could possibly shift/move/actuate after shutting off the engine are A/C components, like blend doors. If you a heavily modified Z with airbag suspension or something like that, then I would look there 1st.
Get a helper to shut off the engine while you're listening under the hood. The brake booster vacuum hose runs from the passenger side of the intake manifold to the false firewall where the battery sits. There's a check valve inline with the vacuum hose between the intake manifold and firewall connection. From there, the hardline traverses across the engine bay under the windshield cowling over to the brake booster where it pops out of the firewall with another rubber hose making the final connection to the brake booster.
That's where I would focus my search, listen to the brake booster and around the check valve and vacuum line connections. The check valve is supposed to maintain the vacuum on the booster when the engine is shut-off. If there's a leak or the valve is failing, then that noise could be the booster diaphragm slowly moving to a neutral position as the pressure equalizes with atmosphere in the lines.
Groaning noise???
