Rippling cones

So after much research and advice seeking here, I made the move to vinyl.
Decided to go with a simple to set up, complete, system as I learn my way. 

I noticed the cones on my KEF LS50s rippling at anything above low listening levels.
This happens only when playing records.   The same music from CD or streaming seems ok (no visual rippling).

Is this potentially damaging to speakers?

Background hiss/pops is noticeable.  Not sure if that is a cause.  This is my first turntable.
My other speakers have grilles so haven't noticed/paid attention to this until rotating in the LS50s.

I pulled the grilles off 3 other speakers and noticed the same thing.

Gear:

Rega RP8 with stock Exact MM cartridge --> Vincent PHO 8 --> Bryston BP26 pre --> Ampzilla 2000 2nd Edition monoblocks

Other speakers tried:
B&W 801 Matrix S2s, Harbeth  SHL5+ 40s, Rogers LS3/5As

There doesn't seem to be much adjustment available on this turntable.

Anyone else encounter this?

Thanks!