This morning this LOUD ticking sound started coming from under hood while cruising. It only comes when i let go of the gas pedal. I revd the engine on neutral but the sound doesn't come on. ONly when i let go of the gas while I'm on drive on tiptronic. someone help please. I'm hoping its not the transmission or the flywheel since the noise is coming from the left side of under the hood cuz that's gonna cost a crapload of $$. HELP!