So your laptop is Windows 10 and MusicBee is your main music app? Just my guess that difference in audio with it open is that it's using a different Windows device interface. You're plugging your IEMs directly in the laptop headphone jack? Generally when you hear hiss with an IEM, it does mean an imbalance with resistance with amp (easier with IEM since it is more sensitive than other headphone types). Also a possible reason since you're only hearing on a laptop's headphone jack (which is using its own onboard DAC and amp). Ground loops can be brought on by all sorts of conditions: perhaps with bigshot's video example, the noise is being introduced by the power draw of the laptop's AC power (fixed at 60hz in North America) vs the powered speaker's draw as well. The earphone ground loop isolator may help: not so much a ground noise filter, but it may have different resistance and may help. If it's a few bucks, it's worth a shot.