You may also want to try the Mic DSP Plugin, if you're on OBS Classic. It's not perfect, but it can improve poor mic quality significantly if you have no other option:
https://obsproject.com/forum/threads/microphone-dsp-plugin.21034/
Be aware, your mic level will show on the System meter (not mic), but your mic volume/mute will still be controlled by the Mic icon and bar graph/slider.
Seriously though, Sennheiser makes REALLY good gear. I'm not sure what's going on with yours.
Make sure it's plugged into the MIC port and not the Line In, if it's not a USB headset? All of the reviews I'm seeing are raving about their high quality, especially the mic. Only other thing I can think of is if the mic somehow either got reversed on assembly as it's noise-cancelling (try talking into the 'back' of the mic; if it comes through loud and clear, this happened). Or possibly if the raise-boom-to-mute switch might have gotten stuck. Try lifting the boom and see if it auto-mutes. Actually, try moving the boom around and see if you get crackle and anything other than handling noise; if you had a weak solder joint or something, it could cause that.
But yeah, check the plugs first. If it's on the aux/line-in port instead of the Mic port, it's not going to work well.