am I now entering another world of obsessive complusive behaviour
LOL - imo its never OCD when you are actually changing the laws of physics and are able to hear it in your room. Vinyl is an electro mechanical vibration resonance hobby.
Try this test Manitunc and anyone else.
Fetch a white plastic juice or other fluid container from your recycling bin.
Using a flat side cut a small piece of plastic out - a little smaller than your leaf spring on the I beam.
Now insert it into the gap where the leaf spring is, making the I Beam more rigid.
Now play a few really familiar records. Do you hear any difference in your room as far as sonics go.
If no change carry on with life as normal.
If you do hear a change and don't care; carry on with life as normal again.
If you do hear a change and are a little curious - do this proper as it costs only a couple of dollars.
Have Bruce send you a couple I beams and loose springs to make into a double and triple I Beam so you have one of each to try with your cartridge or cartridges.
Manitunc have a closer look at all those I Beams you now have. You may see in fact two springs glued together already.
Some may have a small square damper on them while others may be just one naked spring glued in.
What PSI does the ET 2.5 run at?
Ask the person you bought it from what PSI Bruce set it up for. Hopefully he will know.