Annoying rattle

since fitting my rebuilt engine over a year ago I have had an annoying rattle that other TD5 drivers have noticed and have commented on many possible causes. The rattle isnt causing any problems with the engine running but I would like to get to the bottom of it. Today I used my new stethoscope. There doesnt seem to be any untoward noises on the rocker cover so that makes me think its not a loose spring collet or something else on the rocker. There is no rattle or graunching on the idler pulleys as they, the power steering pump and alternator are relatively new. I do have some rattle at the back of the block but that could just be that I am hearing the ignition in the cylinder. However, I can see that the aux belt auto tensioner is bobbing about a bit I renewed this a few months ago asthe possible source of the noise but the movement didnt stop. Ive listened to it with the stethoscope and it does make quite a bit of noise. Is this the likely source of my rattle and if so what might be causing it to bob about so much? Thanks in advance

It could be the crank damper pulley. If you run the motor with fan shroud off and look and listen then you may see some movement in it. If so, take fan off and see if you can get a close up photo to look for signs its separated. Or put a spanner on crank and check its movement.
Mine has a slight wobble and the trapped budgie is there on startup.
Or it could be something totally different....