Water hammer - without changing anything, intermittently

[Jono2]

Recently, a few minutes into taking a shower, I'll hear pretty violent water hammer. It does NOT occur response to changing the valve in any way - not touching anything. It doesn't happen right away and also goes away after about 20 seconds, without changing anything. I'm trying to figure out what causes this.

Possible clues: Hasn't happened in the prior 3 years of use. No other use of water in the house at the time this occurs. I have also noticed that frequently there will be water coming out of the shower head when not in use. The shower is on the second floor and heater is in the basement.

Question:
Because the incoming pipes are pretty inaccessible I'm wondering if it's worth replacing the cartridge first before tearing out walls and putting in arresters?
Thanks!

 

[Jono2]

To prep for replacing the pressure-balancing cartridge, pulled it out, but not a brand name in sight. Does anyone recognize it>

 

[Sponsor]

 

[Terry]

How about a picture of the handle? I'm sure someone here will know.
The hammer could be in the balancer portion of the cartridge.

 

[Jono2]

Thank you! I haven't seen the knurled post coming out of this cartridge before. Google lens isn't coming up with a match for the face plate either.

 

[Terry]

Product Detail

Get support for your Marielle R89-1MB 1-Handle Tub & Shower Valve Only Trim

www.pfisterfaucets.com

Product Detail

www.pfisterfaucets.com

Maybe?

 

[Jono2]

That's it! I think it has this extension on it that was throwing me off.... and the top trim ring is green, but pretty sure that's it (Pfister part 970-0770)

https://www.amazon.com/dp/B01JTGQZPO?ref_=cm_sw_r_cp_ud_dp_BVPSE23W3XA91RSJVJGW

 

[Jeff H Young]

Yes Id say a cartridge change would be smarter than tearing open walls.
How much pressure is there? is there a pressure reducing valve ?