Bell & Gossett Flo Control Valve SA-1 - Inside Noise

ZBoiler

My house is heated with hot water. Lately, I started hearing a scratching noise inside of Bell & Gossett flow control valve SA-1 that resonates slightly through piping. What could be the cause and should I be concerned about it, especially, if the house won't be attended for the next month or so?

STEVEusaPA

Air?

hot_rod

Nothing else changed in the system? Low flow rate can keep it from opening completely.

Simple inside, a weighted plug that lifts up when flow starts.
https://media.statesupply.com/filemanager/1/9/19012015-bg_flo-control-valves_instructions.pdf

ZBoiler

Nothing changed and there isn't noise anymore today. A manufacturer rep suspected a piece of stuck rust debris could be the cause.
Thank you.