Water Hammer Arrester Replace
A water-hammer arrester is an (initially) air-filled container that simply acts as a compressible &quot;shock absorber&quot;. Over time, the air can dissolve in water and be lost, particularly on older models without pistons, leaving it filled with pretty-much incompressible water. They're easily fixed or replaced.
If the existing arrester has replaceable O-rings:

Close the main interior shutoff valve.
Turn on faucets in the lowest floors to help drain the system.
Get some buckets and towels to soak up water, and place below the arresters.
Unscrew the arresters, disassemble them to drain the water, and check for damaged O-rings.
The O-rings can be replaced at very low cost. If possible, find the right size O-rings in advance or get an inexpensive assortment to shorten the downtime.
Reassemble, turn on the main shutoff and test the system.

If the O-rings cannot be replaced, by design:

Replacement arresters are available for US$10 each and up. Follow steps 1-4, above, and at step 5, replace the old arresters.