The Technics' weighted s/n figure is -78dB. This is lower than most turntables under $4K that publish their spec. However, perception of turntable quietness is not so simple, and subjectively the Rega P3 *sounds* quieter than the Technics. I don't think this is belt drive vs. DD as much as other factors. The Rega P3 variants have had about 25 years of development in vibration control and resonance neutralization. Those developments in the Technics stopped with the 1981 introduction of the sl1200mk2, still in production.
However, I've found, as a Technics owner for 2-1/2 years, that some simple, inexpensive things can control resonances and vibration in the Technics that subjectively drop the noise floor, improve inner detail, clarity, and dynamic range, and relax the presentation.
Out of the box, the tonearm rings: wrap it in Teflon plumber's tape. Replace the feet and replace the turntable mat. This $42 in tweaks takes the reputed "direct drive glare" right out of it. I've found that much of this glare is tonearm resonance. It rings right in the upper midrange, and the $2 teflon tape pretty much fixes it without significantly changing the effective mass.