loud diesel clatter

Sure one piston could be causing it. When the piston was replaced was the cylinder checked and was the piston/rings sized properly? How about the other pistons and cylinders, what condition are they in. You need to measure them not just look to tell.

Joe, I have a Golf which had a bad chatter. Much to my surprise I found it to be the waterpump. I had NO leaks but the shaft could be in and out more then an acceptable amount. I removed the pump and found where the propeller had been hitting the inside of the pump housing. I you have the tools and time to replace the pump assembly enjoy the experience. The injector pump and bracklet has to be removed. The noise from the waterpump travels well in the block. I had 153K miles when I changed mine but had been making noise for months. I hope this helps

Joe, In my last reply I failed to mention one other common problem that is the bolts holding the A/C compressor to the mounting bracket. This bolts break or work their way out periodically. They are an 8mm allen head and easily seen. I've had problems with them in the past. If they are broken be prepared to spend a little time. They can be removed without removing everything with a little patience. I hope this helps.