My 2010 V6 Mitsubishi Outlander VRX has travelled 64,000 km and has been serviced at regular intervals by Mitsubishi. It has developed an engine noise that sounds like a low "dong" noise. Mitsubishi have looked at it twice, the first time saying there was no noise, and the second time replacing "the noisy charcoal canister". The noise remains. After the car has warmed up and in a stationary drive gear the noise is most noticeable. Do you have any clues as to what it could be?
Without listening to the engine and hearing the noise I couldn't speculate on what it might be, but any mechanic worth his sale should be able to give you an accurate guide as to where the noise is coming from and what might be causing it. What you appear to have been told by your dealer sounds like complete rubbish to me, a "noisy charcoal canister", really. Take it back to the dealer and demand their proper attention to the problem.