scion xD engine rattling problems question

i have a scion xD with a rattling engine. took it to the dealer and got quoted for a whole engine replacement. talked with a few mechanic friends saying it could be just a tensioner/timing chain problem. sound only comes around when i step on the gas. releasing gas or revving the engine while it's in park can't duplicate the sound. thoughts? via /r/cars http://ift.tt/2s3GAkQ