Apartment Hydronic Heating Noise Question

Hello,

I have a quick question about a rattling noise coming from one of the pipes in my apartment heating system. I'd like to see if there's anything I can do to fix this noise before contacting my landlord.

As mentioned in the thread title, I believe this is a hydronic style heating system. Here is a pic: http://i.imgur.com/CPC9u2B.png

I noticed that there is a slotted port on each of the individual pipes (see pic: http://i.imgur.com/7qbDZE5.png ). Since this noise is only coming from one of the three pipes in my apartment, would it be possible that temporarily loosening this slotted port would fix the problem? Or would that choice be ill advised?

Also here is a link to an audio clip of the noise:

Thanks for any help you can provide.