I have been going mad with these underground vibrations, and it's only today that I finally find someone else who can feel them!
Can you still feel them now? I felt them start exactly on 1/8/21 at 6.00pm, on the dot. (I don't live in your area but in E1). They stopped in November, and I thought it'd be it finally, but in December it started worse than ever. I feel nauseous, can't sleep properly, it wakes me up at night when I do finally fall asleep, and it does seem like being on a boat on rough sea. I am also getting frequent headaches.
It's a constant tremor, with some sideways lurches every now and then. Occasionally stops for 15-20 minutes, then starts again, and I find it particularly bad between 5pm and 5am. It's the equivalent of a pneumatic drill, without the noise, just the vibrations.
I don't have the tube below, and in any case, as you already pointed out, it's not a tube noise, with trains coming and going. And the tube has been there for decades, not since 1/8/21. I started thinking of tunnelling.
I contacted some companies: TFL and Crossrail don't have any tunnelling going on at the moment, but London Power Tunnels does. Do a search of their name and map or route, and you'll find a map of their tunnelling all below you in South London. I have exchanged emails with them, and obvi they deny that their tunnelling can be felt by humans (I guess that makes us aliens then), let alone in E1, even though they admitted starting a new tranche (or circuit like they call it) of digging in August, exactly like I felt it happen.
Are you still feeling these vibrations? We could share the information we have; I could share the emails they sent, and perhaps can find a few more people that feel this. I would like to be able to find some way of measuring and recording this vibrations, like ronangel suggests it's possible, finding out exactly who it is, London power tunnels or others; and ideally be able to obtain a legal way to stop them working at night.