It is the most common complaint in the first fortnight after an install, and it is a description of the unit working correctly.
What the squeak actually was
Hard water contains dissolved calcium and magnesium. Soap reacts with them and forms an insoluble curd — soap scum — which does not rinse away. It deposits on skin, on hair, on the shower door, on the bath.
That deposit is what produces the "squeaky clean" feeling. It is a thin film of reacted soap sitting on your skin, and generations of people have been taught to read it as cleanliness.
It is also the same substance that leaves the ring around a bath and the film on glass shower doors.
What changed
Remove the hardness and there is nothing for soap to react with. The soap stays soluble and rinses off completely, leaving your skin's own natural oils behind.
Skin with its oils intact and no soap film on it feels slippery. That is the sensation. It is not residue — it is the absence of residue.
Use much less soap
The other half of the adjustment, and the one that saves money.
Soap lathers dramatically better in soft water because none of it is being consumed forming scum. Most people carry on using the same amount out of habit and produce far more lather than they need, which makes the slippery feeling more pronounced and takes longer to rinse.
Try roughly a third of what you used before. Shampoo, body wash, dish soap, laundry detergent — all of it. The laundry saving in particular is noticeable over a year.
The other early observations
Soap scum stops appearing on doors, tiles and taps. Existing buildup does not vanish on its own, so there is usually one last proper clean before the problem retires permanently.
Spotting on glassware changes. Hard-water spots are mineral deposits left behind as droplets evaporate; those stop.
Skin and hair often feel different — less tight after a shower. This varies by person and is not a claim, just the commonest report.
If it never becomes normal
Some people simply dislike it, and that is a legitimate preference rather than a fault. The usual accommodation is to leave a tap or two on unsoftened water — often the kitchen cold tap and the outside taps, which is worth doing anyway so you are not softening water for the garden.
That is a plumbing decision best made at install, though it can be retrofitted.
If the slipperiness stopped and you did not change anything, that is a different story — it usually means the unit has stopped regenerating. The four checks take about ten minutes.