The bias may cause this issue, my guitar tube amp had some pretty bad sounds till it was biased after I replaced the tubes. Can't say for sure that's the issue in your case, just that it may be one of the causes.
Are you getting any audio or just the noise by itself? Noisy audio or regulator transistors could cause static noise. If your soldering skills are not practiced excessive heat can damage components. Get a VOM and set the pot according to the instructions. It's may be to adjust DC to zero at the output which would not cause this kind of noise with no input signal. You can use the VOM to check the transistors too,