That doesn't sound right to me - seems you have DC on the output of the last opamp. Maybe try swapping the ICs and see if the problem goes away (U3 & U4). Or you could add a blocking cap but it would be better to just get opamps with the the output Vbias.fazeka said:I am still getting noise when switching.
About the high frequency - these are pretty noticeable. You might want to measure the frequency response (I posted some sweeps back on page 9). I'm guessing there is something wrong if you aren't hearing them, especially with the 12k & 16k. The stock 20k is very noticable because the HF boost is full at 20k but has a wide boost all the way into the high mids (~1k ~2k)