[911medic]

OP, I had the same issue with noise as you when I put my RX breather on and removed the stock clean side breather tube. I ended up putting my stock setup back in place as I was afraid I was going to wreck a seal somewhere with the excessive vacuum in the engine.

The problem with removing the check valve, as you did, is that the valve serves 2 functions. First, it prevents crankcase gasses from venting to the atmosphere, and second it is supposed to meter the incoming air. Since you've removed this meter, you now have unchecked airflow entering that breather, which is eventually drawn into your intake manifold via the PCV system.

The problem is that this air does not pass the MAF sensor and is therefore unaccounted for by the ECM. This can screw up your fuel trims and cause issues.

Supposedly some were able to get replacement breathers/check valves to remedy the issue, but in the end I decided it wasn't worth the hassle and just removed it.

I've been periodically checking my intake tube for signs of oil ingestion and haven't seen any yet, although I did have some prior to installing my catch can and drilling out my PCV valve.