Hey everyone, I posted about heating systems awhile ago, but I have another simple question. I have an old school heating system in my building that looks like this:

It hisses ridiculously loudly almost all the time. The hissing is coming from the valve on the right, which I turn to turn on the heating and turn it off, and the vent on the left (which on mine is kind of shaped like a bullet), which seems to let out a lot of steam. It is a really grating, unbearably loud noise, and all the steam makes my apartment really humid. I'm also on the top floor of the building, so I get an additional steam vent at the top of the big pipe that runs the building.
My question: I noticed that I can muffle the sound significantly when I put a towel over the vents and loosely wrap them. It also soaks up some of the steam (I am worried about water damage). Will this a) mess up my heating system b) cause my apartment to blow up or something worse or c) do nothing except muffle this awful, awful noise? I hope it's c, but if you know otherwise (especially if it's b), please let me know!
Thanks in advance.