Hi,
Have you noticed a loss of power or performance? Is the sound from outside the vehicle, possibly under the vehicle or the engine compartment?
When you hear it, take note if it changes with throttle pressure. For example, if you are accelerating light is it different than if you are quickly accelerating?
If there is a power loss, you may have a blockage in the exhaust, likely a catalytic converter. If you remove an oxygen sensor before the converter, you would know if that is it because the added release of air would likely stop the noise. Here are a couple links you may find of interest:
https://www.2carpros.com/articles/bad-catalytic-converter-symptoms
https://www.2carpros.com/articles/how-to-test-a-catalytic-converter
Let us know.
Joe
Friday, August 21st, 2020 AT 9:11 PM