Well I have wondered for a while if instead of replacing them I should try and clean them first, Like many I do have that hum/moan when shutting down and whilst it doesn't worry me I were hoping it'd stop it or reduce it. It didn't nonetheless. Pretty easy and quick to do, I removed the air box for ease of access loosened the lower nut and removed the top nut. It'll slide out of the bracket and you're left with an electrical connection and two hoses. The cap is exactly that and you pop it off to reveal the filter inside. As expected it's dirty and it washes out easy, I noticed the rear valve were dirtier than the front one. Shame it didn't do much and if I could take a stab at something if anything were different I'd say the turbo had a bit better response, but that's only a guess.
Would I do it again...... Probably not, it weren't that dirty nor has it made a difference.
