Twenty years ago we installed a Master FES-10T to treat water hardness and prevent plumbing corrosion. This unit was no trouble until it started leaking in mid-2010.
A local plumber replaced the old unit with a Master NS-10T, a mistake because it did not eliminate iron in the water. Both the plumber and Master's local distributor know little, if anything about water softeners.
The new unit caused "air hammer" which the plumber could never eliminate. Called in an area well drilling firm regarding the "air hammer". They advised that Master softeners are extremely noisy when in operation and there was nothing they could do to correct that problem.
The air hammer problem is therefore actually built into the Master softeners. If a Master softener is installed in a house, be prepared to live with the air hammer noise.
Also there is no CUSTOMER SUPPORT by Master whatsoever.
Editor's Note: we have sent details of this story to the company, and welcome comment from employees or directors of Master Water. The company's website is so poor that it doesn't even have a phone number, even less a customer services email address. You can reach the company on (610) 323-8358.
Meanwhile, here's a video about improving the air hammer/ banging pipes problem if your house suffers from it.