Because they do it all the time, and have since the Soviet Union days.
"Despite multiple upgrades, the veteran aircraft is still limited to its old-fashioned airframe. The bulky turboprop plane is not only very visible to various radars, but it also makes a lot of noise.
" “The Tu-95 is the ‘brightest’, it’s the noisiest among our planes. It’s so noisy with all its propellers and four engines that even an underwater hydroacoustic system, resting on the ocean bed and used to track submarines, hears the noise of a Tu-95 flying at a 10km altitude,” according to Lukashevich."
I'm reminded of the surprise from seismologists when they discovered the phantom squiggles on their charts were tornadoes touching down. I'm wondering if they can detect these bombers?