Leaking Air Sound

First off, I apologize in advance for this poor description, but my father's 2nd Gen. 4-cylinder Tacoma is starting to emit a strange noise at very low RPMs. It's especially noticeable at low RPMs (between 750 - 2000 RPMs) and it'll sound like air is escaping somewhere (perhaps from the exhaust manifold to the flex pipe?) and then a sort of rattling noise as if a heat shield or a metal part is loose.

This also happens when we encounter inclines and more noticeable when the car is under load.

I've checked the heat shield around the CAT and I've sprayed soapy water around the area where the flex pipe meets the exhaust manifold but there is no air coming out.

Again, I apologize for using any incorrect descriptions as my car knowledge is very, very basic.

Has anyone else experienced this and what could be causing this? We did have a clogged CAT that we fixed recently (by changing the sparking plugs, cleaning the throttle body and running a few tanks of high octane gas from Chevron).

Thank you in advance.

 

This caught my eye. Did you have a code for catalytic converter efficiency that lead you to try to fix it using this method? Asking because I don’t think the procedure you described can really fix an actual problem with a catalytic converter.

Did the noise come on suddenly, or has it been getting worse over time?

Since it happens in the lower rpm ranges, can you use a stethoscope to try to pinpoint the noise while parked? You might need a helper to step on the gas to get the RPMs up a little bit. I would recommend against putting it in gear and power braking (assuming you have an automatic) as that would be dangerous.

 

Spark plugs and higher octane gas won't unclog a converter. Once they're clogged, they stay clogged. The hissing sound could be an exhaust leak trying to get around the blockage in the exhaust.

Get your hands on a exhaust backpressure gauge and see what you've got

 

Did you check for snakes?

 

Will do this weekend, thanks for the suggestion.

 

Snakes are only on planes! J/K, thanks LOL!

 

Sounds good, thank you!