I recently purchased an MDX (1K miles so far) and have noticed a loud tapping noise when the A/C is on. The noise subsides when the A/C is off but I can still hear the noise. I checked the oil level, just to be on the safe side and it seems ok. I know honda engines are suppose to be extremely quiet, so I'm a little perplexed about the noise. I'm going to take it to the dealer this week. I'll keep everyone posted.