If you do Atmos stuff the 300s and move the Ones to another room / rooms.

Unless your low end wasn’t good (not enough or uneven levels) when the old Sub was working properly adding a second won’t likely improve much. Contacting Sonos about replacing the one that is acting up might be a very good plan versus just buying a new one.

thanks for the reply - will look into contacting support at some point.

the old sub works under normal load - no rattling, only when it hits very low frequencies, loud volumes (e.g. big movies) . 

thanks for your perspective, that  a second sub doesn’t add that much more to the immersion , compared to what the 300s can bring (atmos).. 

there aren’t a lot of atmos content though ? if the occasional movie now and then, and then more for music listening, would the second sub be better ?

I’m finding a fair number of movies on Amazon, after the $2.99 premium charge.

Same for Amazon music, finding Amos format stuff is hard due to there being other things Atmos that search finds but what I do find sounds good.

I wouldn’t pay a lot to upgrade to Atmos at this point but I’d sure make sure it was included (if available) in anything I upgraded for other reasons.

ok so I have contacted support, 

we have isolated this to a problem with the sub,  because I managed to replicate this when the gen 2 sub was connected to the Beam. 

now they are offering a discount when I send back the gen2. 

but I'm thinking - keep the gen 2, get another (gen 3 ) sub, and then hopefully the rattling will not be too pronounced (move it further away from MLP) ? end up with 2 subs