I am very tolerant of many different flavors of system sound, but I have very low tolerance for noise of any kind.
If I put my ear up to the speaker and hear anything other than silence when the system is on even if only at higher than normal volumes and nothing is playing, I consider it a potential problem, even if practically it is not apparent during normal listening.
I agree with Tvad that noise can and often does have a negative effect on overall sonic performance when present even if virtually impossible to hear flat out.
If I put my ear up to the speaker and hear anything other than silence when the system is on even if only at higher than normal volumes and nothing is playing, I consider it a potential problem, even if practically it is not apparent during normal listening.
I agree with Tvad that noise can and often does have a negative effect on overall sonic performance when present even if virtually impossible to hear flat out.