The sockets I normally plug into are all on RCDs but I expect as this coupling is not causing current loss from the primary side they would not register this as a fault.
You can touch it with one hand and touch someone else with the other and feel the electricity.
This is indeed genuine leakage current coupled over from the primary side and it is sensed as leakage by the RCD, but the current is much to low to cause a trip. You can feel a fraction of a milliamp order some conditions, and many PSUs are designed leak that much. The actual leakage amount is a compromise between reducing radio interference and leaking enough to be annoying (but not in any way dangerous.) By the time you get up to 'fault' levels high enough to trip an RCD (tens of mA) that is quite a hefty jolt, not just a tingle.
I've had musician friends have trouble with earth loops causing hum and buzz in sound paths because there were too many earths
There are usually better solutions than disconnecting the safety earth. Having worked in professional audio for many years and designed and wired a lot of studio equipment, I can honestly say that I have never had to leave something floating, I have always been able to avoid the earth loop some other way. Hum problems are also often blamed on earth loops that are actually due to something else entirely,
It's interesting because in the US where it's designed they don't use ground pins -
As Megawatt says, all modern US installations have grounds everywhere and grounded outlets have been in use for 100 years. There is some important history behind the 2 / 3 pin plug adoption and it's as much a European thing as American. Basically most plug/socket systems allow for either 2- or 3-pin plugs and mains adaptors, that fit into 3-pin sockets. In the US if your device doesn't need a ground, it has a NEMA 1-15 2-prong plug that fits a 5-15 or 5-20 3-prong receptacle and simply doesn't use the ground connection. This is what you see on chargers etc. But a grounded appliance will have a 5-15 or 5-20 3-prong plug fitted as standard.
Likewise in Europe a double-insulated low-power appliance gets a 2-pin Europlug that will fit any of the European variants that have pins on 19mm centres, and just ignores the available earth contact whatever form it happens to be. But class I appliance will be fitted with the locally suitable earthed plug.
In the UK we used to have both 2- and 3-pin round-pin plugs in all three current ratings (2A, 5A and 15A) but they were not compatible. The line and neutral pins were the same size but the 2-pin version had slightly smaller spacing between them. So a 5A 2-pin plug could only be used in a 5A 2-pin socket. Then in 1947 we had a major re-design and got rid of all of those old systems, which is something very few other countries have done. At that point we introduced mandatory safety shutters that were, at first, always operated by the earth pin, so there was no possibility to include a 2-pin 13A plug variant. It's the only system where one has to use a bulky 3-pin plug even for tiny appliances with 0.1A load and no need of an earth. If you regularly use USA and EU plugs as I do, you come to see that as something of a drawback.
