Rega Planar 3 RS into Sonos Play:5 - mild rumble

Rumble is usually a platter bearing issue with the turntable.

Can you give us a better description of the sound and exactly when it is present and absent. 

It’s a rumble you can feel and a low frequency. 

What we usually describe as “turntable rumble” is audible or measurable through connected electronics only when the stylus is contacting a rotating record. Other noises are possible, for example, if the shelf supporting the turntable is vibrating due mechanical coupling to a heater system, there may be noise output through the system when the stylus is sitting on a stationary record.

If you are hearing or feeling vibration directly from the turntable while the tone arm is locked, I suspect that the turntable is not correctly setup.

Repeating some of the above.

Any chance it is not a turntable bearing related rumble but a 50 or 60 (depending on your power) cycle hum? That is a steady sound, not varying if the turntable platter is spinning or not.

Possibly vibrational feedback from a poorly isolated/supported turntable? That is greatly reduced if the stylus is lifted or the speaker volume is reduced.

Almost any option other than a rumble is hoped for as aside from a very few high end turntables the cure for rumble is to discard the defective one and purchase a new one. I've only seen one case of rumble, the owner shipped the turntable without lifting/securing the platter and the bearing was deformed, creating the rumble as the imperfections aligned as the platter rotated. You could actually feel it if rotating the platter by hand.

The platter bearing support is mentioned here in the unpacking steps.

https://www.rega.co.uk/download/Planar-3-RS---User-Manual-EN---Ver-1.pdf

Interesting that with all the specifications given above sound quality ones are noticeably absent.

Read a half dozen reviews and all were nonsense, impressions, feels and audiophile foolishness. Couldn't find one solid review with measurements of the audibly important features. Rhapsodising over the meticulous preparation of the drive belt is not a substitute for wow and flutter measurements!

Assuming you’ve setup the Rega Planar 3 RS correctly...here are my Comments/Questions:

Comments:

The terms Hum and Rumble are subjective to the the person describing what they think they are experiencing/hearing/feeling. Both cam produce a vibration of sorts so here again IMO the terminology is subjective. 

Questions:

1. The cable between the phono pre-amp and the Play 5 look like the one shown below with two (2) black rings on the 3.5mm end...correct?

2. You are using the stock MM cartridge supplied with the turntable and not an upgrade to a MC cartridge...correct?
3. In the room with the Play 5 the Line-In settings are as shown. Although you may have to experiment with different Source Levels

4. Audio Delay is recommended to be set to Max 2,000ms as shown

5. Autoplay Room should be the room that contains the Play 5. I recommend an Autoplay Volume less than 50%

Conclusion:

If all are set correctly then you may have a defective turntable 🤔

How close is the Rega TT to the 5? 

The difference between hum and rumble is easy to recognize after a bit of listening to the two.

The key things for hum are that it is a constant frequency (matching your power) and it rarely varies in amplitude unless you move something.

Rumble is irregular in nature and the individual peaks of sound often vary in amplitude. Depending on the severity of damage to the bearing the overall amplitude can vary from near silence (the damaged bits not making contact) to quite loud (damaged bits of bearing and race aligning.) 

One may be able to find examples to listen to on an audio or video site with a good turntable section.