In my year of Volvoing I have had 4 instances of bad timing gears (or variations thereof) which resulted in keep knocking noises that sound EXACTLY like rod knocks, only occuring at different times and under different conditions. I've actually had a rod knock only once (after about a year of 7K rpm zings on a shade-tree rebuilt bottom end). It sounded about the same.

Cam knocks (from bad gears or worn thrust plates allowing the cam to knock back and forth) - knocks at idle, and fades as the rpms rise.

Rod knocks - can occur at any speed, more sensitive to the load on the engine, quets down more at idle. When I had the spun rod bearing it was perfectly quiet at idle, unless I pulled the #2 plug wire - at which point it would start gently knocking again.
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I'm JohnMc, and I approved this message.