Injectors will make a very light snapping or ticking sound. If what you're hearing is more of a hard metallic clacking, it's lifter noise which is pretty common. That's not to say it's acceptable.

Breifly, I had one lifter that was noisy also and as the ambient temperatures weren't above 68F as per the manual, I changed to 5W30. I had just recently bought the car with 77,000 miles and wanted to change the oil anyway. I used a can of engine flush I found at the local auto parts place, drained the old oil, the cooler (turbos have an oil cooler) and added the new Mobil 1. The noise went away. Recently, ambient temps here in Memphis climbed above 68F so I changed to the recommended 10W30, again Mobil 1, and haven't heard the lifter yet. I'm hoping for the best.

If it does return, the next step is to replace the 0-rings on the oil pickup tube and filter galleries in the oil pan. They can deteriorate and allow just enough air to drawn up by the pump to prevent the lifters from pumping up correctly.

If that fails then it's time to replace a lifter.

Go to Volvospeed.com and search the maintenance bulletin board for more information. A VERY good source.
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Erwin in Memphis, '95855t, '86 Guzzi LeMans, '76 Montesa 348 Cota