Well, it's different to mine as your one lives outside the car it doesn't need to be as quiet. I assume you didn't buy a new compressor? If that piece flows air nicely then it should be fine and I expect your other one is too.
Start with the basics. Take that part out of the currently fitted compressor and test it, it will be loud but it if it works fine then your issue is there and it probably needs cleaning out but I don't see value in drilling extra holes in that type of silencer, it won't clog like the brass ones.
I'll keep coming back to the drier unit though, we need to know if that is new or not. Basically your car is telling you it can't vent enough air when it expects to so you either have:
A blocked silencer (unlikely seeing what it looks like)
A clogged drier unit
A non-working exhaust valve - that usually presents a different error although I have no idea on the code but it's in my linked threads.
The Discoveries and RRS can suffer from the compressor bushings failing which you'd have seen when you replaced it I expect but in case you didn't or they aren't that bad yet, it's worth checking the wiring to the exhaust valve as I have seen them chafe on the bracket. It doesn't always rub through the wire but it break down the insulation and then you'll get high resistance and poor connectivity on the exhaust valve which might also cause this problem. If so yo need to cut out that wiring and solder in a replacement section with heatshrink and proper insulation, don't bodge it with crimp connectors or you'll be doing it again next year!
EDIT: Just realised this reply isn't to the OP, is it two of you with the same issue or are you both working on the same car? Most of this still stands of course, just interested to know.
