IWE question, noise on decel gone in 4wd and worse on brakes

[fur_pig]

New to me 2018 has a very slight grumble at low speed decel when i'm on the brakes (using vacuum for booster I guess). It goes away in 4WD. Is this typically the check valve, IWE valve itself or a line (or a total guess)? I don't have a ton of time to diagnose and would rather throw a cheap part at it but wanted to get the experts opinion first to point me in the right direction. It is not grinding and almost feels like when you drive a big truck with an electric air brake booster that kicks in.

Thank you in adavnce.

 

[smurfslayer]

start using 4a regularly until you get the issue diagnosed and addressed, it will prevent further wear and tear.

usually the solenoid is the ubiquitous first replaced part, it’s inexpensive and readily available. If it’s gone on for a while you might need some hard parts though.

 

[nikhsub1]

Replace the check valve it’s at the brake fluid reservoir