Engine Sounds like a Diesel when not in Gear?

[ArioKenBuddha]

Engine Sounds like a Diesel when not in Gear? Don't know what the issue is. It sounds fine while in Gear. Super loud when not. Any one else ever experience this? It doesnt sound like lifter noise. Tranny?

[dawagarage]

that isnt too great of a description.
what exact system sounds like a diesel? the exhaust?

whats your approximate rpm?

[tacobellman_2007]

Pop the hood while the car is running and move around each of the fuel injector wires. See if anything changes. I had a similar problem with my car and it turns out that one of the fuel injector wires was a bit faulty, because wiggling it around to the right position made my engine idle much better. Lol. Still have that wire, and still in that same position :P

Could also be one or more of your spark plugs?