Resonance in pipes, heating system
I suspect that you have a warrantee issue with the Armstrong pump.  Sounds like yours has a bad bearing or out-of-balance coupler, it happens. Normally these pumps are quiet and reliable. I wouldn't let this slide.  I suspect that the pump will experience a significantly shortened life if left in service.  FYI, there is a new class of hydronic pump on the market today.  I think it is superior to this type of pump.  They are call 'Wet Rotor'circulators or 'wet rotor' pumps.  They are actually quieter and more reliable than this style of pump. The cost is similar. And they experience fewer service issues.  Most of the major manufacturers offer this new style. Taco makes a good one and Grundfos too, however all of the major manufacturers make good products.