As I have found, even though they are heavier, the aluminum bolts are louder. My theory is that there is an echo effect from the hollow metal tube flexing with the shot.
There is a way to quiet that echo chamber effect with aluminum shafts, but it does add some weight.
Materials list: Get a block of that light foam florists use to make floral arrangements, and a 1/8" dowel.
Remove the inserts fromyour shafts. Push the insert end of the shaft through the foam. The shaft will cut it's way through the foam and form a plug inside the shaft.Use the dowel to push that plug all the way back to the nock end. Repeat the process until the shaft is filled.The more the foam is compacted, the more foam you put inside, so to keep the arrow as light as possible avoid compacting the foam any more than absolutely necessary to get the inserts reinstalled.
This works great on full length aluminum arrowsI used on my trad bowsand I see no reason it won't work equally as well on crossbow arrows. Unfortunately, Idon't knowthe grains per inch that foam adds to a 2216 or 2219arrow. It's been a long time since I've done it and I don't think I ever weighed an arrow afterwards anyway. But it really does eliminate that metallic twang that an aluminum arrow makes from time to time.