My two penneth..
I had exactly the same "chugging"/"diesel"/"marbles in a tin can" noise on my car, but
only when warm. From cold start up it was quiet as a mouse. If you guys are experiencing the same noise,
only when warm, I'd put a few quid on it being the same issue, but thats just my opinion!
After much research, watching videos similar to the ones here and reading posts similar to this one, I bit the bullet and changed the chain and tensioner (well, had it changed by a garage). Not because I knew for sure it was the culprit, but because I thought there was a good chance of it and if it was the chain/tensioner, I didnt want to leave them to get potentially worse. Also I figured If anyone was going to get as far as looking at these parts to see if they're failing (condition might not be easy to judge anyway - i.e. I'm told tensioner sits on a ratchet when engine off so difficult to gauge its condition), they may as well replace them whilst they're in there! My luck was in and now my car is quiet as hell (comparably, anyway) warm or cold.
Its a tricky one I know, there are also plenty of people who say their car has made the noise for ages and been fine, but I couldnt stand it!
Not sure if this post is helpful, just though I'd stick my oar in!
