Why Rumble One Side of Album

No need to put up with the rumble! Either you pursue a phonostage with rumble feature built in or try this device. Many here have tried this device on @roxy54 recommendation and have great success in eliminating rumble,

https://www.kabusa.com/frameset.htm?/rf1.htm

@vonhelmholtz , unfortunately, this is a very common problem. The masters of  the sides may be cut on different lathes. A lathe can rumble just like a turntable. All the stampers made of that master will have to same rumble so generally all the records from the same supplier will be affected. I must have at least 50 discs that have embedded rumble. They are all modern pressings made on old lathes that have not been maintained well. I am not entirely sure but I do not think anyone is still making new Lathes.

My KAB RF1 arrived today.  I recently bought a Boz Scaggs Greatest Hits Live record that made my woofers look like they were going to jump out of their enclosures.  With the RF1 there was NO woofer pumping whatsoever. 

The clipping indicators on my amps often flash (I think they are overly sensitive!) when I play vinyl.  I turned it up louder than I usually listen and they did not come on at all, so it appears to have lightened the load on my amps also. 

I only listened for a few minutes (work and all that) but didn't notice any degradation of sound.  I'll be able to do some extended listening later this week.

OP,

Is it always on the same side?

@big_greg , I have a very effective digital  rumble filter 80 dB/oct @ 18 Hz. I would estimate that 2/3 of the rumble is above 18 Hz and clearly audible on many discs. Pushing a rumble filter up higher destroys your bass especially if it is analog. Having a rumble filter is no excuse for the people cutting lacquers on poor lathes.