Is customer support at sonos terrible?

Sorry, but this is simply not true. The basic laws of physics mean that radio signals can interfere with one another. If that meant the equipment was faulty then every single transceiver, including every mobile phone in the world, would also be faulty.

A simple example: try using Bluetooth earphones adjacent to an operating microwave oven. Both use the 2.4GHz band, but don’t cooperate. The radio frequency noise emanating from an oven is more than sufficient to disrupt the delicate flow of information over a very low power Bluetooth connection. The same is true for a 2.4GHz WiFi signal. 

Some reading matter:

https://en.wikipedia.org/wiki/Electromagnetic_interference

https://en.wikipedia.org/wiki/Inverse-square_law

Ratty, 

Again missing the point, for instance there could be interference and a button not work as the solder connection has been broken. Thus the equipment has interference and is faulty. 

Honestly I am not sure I can make this any clearer….

Are we having a semantics war? We thought we were discussing unfortunate electromagnetic interactions that prevent successful communications between units, not mechanical failures that “interfere” with proper operation.

‘I have tried to find a resolution today for my SL one as it keeps dropping out whilst the others are find, playing music delayed and having reverb. Sonos say its interference, though all other sonos equipment works. 

They have been quite rude and instead of escalating have left me on hold for 90 minutes to then hang up. ‘

Semantics, we aren't even talking about the same thing anymore… 

All my equipment from sonos works, bar this one, even moving the equipment it still has the same issue, which means there is a fault with the equipment. Sonos refuses to take ownership and blames microwaves, though all other equipment works fine. I am then left on hold, until the day ends and they hang up. 

Be realistic, stop avoiding the point and what you are adding is going round in circles on a problem which is not highlighting the issue. 

Do a controlled test. Swap the ‘faulty’ unit with one that doesn’t suffer from any issues.

finally, already completed test, no issue. 

Faulty system still has issues when placed in another room. 

Does that speaker only suffer when it’s grouped with others? 

If so, does it make a difference whether you (a) start from that room and add others, or (b) start from another room and then add that room?

wouldnt be able to tell on the delay as need more than one to play for that, though still get the drop out, even when main speaker on grouping or on its own. 

Temporarily wire that speaker to your router with an Ethernet cable and wait 5 mins for the system to re-adjust.

Does it still drop out when played on its own? 

Temporarily wire the unit to your router.

(Oh well, I type slowly)