The Harris can be attached to an AR with round handguards by means of a small accessory that is widely available.  Accessory is inserted through a vent hole in the handguard, from inside out, and the bipod is attached to the projecting portion of accessory.

Try pouring some lead shot or bullets into the buttstock compartment of your AR and trying that first.  The store-bought stock weight is kind of expensive for just being a hunk of lead.

Cant help much on the spring; never was a problem for me.  Most folks keep 'em clean and well-lubed.  That seems to cut down on noise.