By your description you could have some dust or other contaminant that is causing a discharge. If so it should subside over time.
I’ve had variations of random noises caused by contaminants over the years with the various SL panels I’ve owned. The noise, with no music playing, can take the form of crackling, sizzling, whistling, ticking, etc..
At times I have been able to change the characteristic of the noise, or even eliminate it, by standing close to the panel and blowing hard into the area where the noise emanates. You might be able to use “Dust Off” canned air to provide the same effect, just don’t point the nozzle too close to the membrane.
The PX panels are very reliable, Roger has mentioned in the past the only issues they’ve had are due to shipping damage.