Probably wheel bearings or wheels are unbalanced
check the crank shaft actuator?
It could be the fuel pump, if its when you first start the car up
Taking your foot off the accelerator.
As the vehicle sits idling the driveshaft is not rotating.
Yes, when idling and driving.
It depends on how long you are idling, or how fast you are going. If you know you are going to be idling for a long time, it's best just to put your car in park.
In order to tell you that you would have to describe the noise and what the car is doing when the noise is made. Are you idling, driving, just turned the AC on? What is occurring and what is the noise? Idling and sounds worse when AC is on. Sounds like it is coming from the top of the engine. Vehicle has 120k miles
Car emissions can be reduced by reducing idling time and by driving at a moderate highway speed when possible. Driving too fast and idling are both wasteful in terms of fuel, and increase the vehicle's emissions.
It's a 1997 Tahoe
It is idling. This is hard for an engine to do smoothly.
choir members in your pipes
You need to check the operation of the radiator fan.