Bose S1 PRO PLUS hissing sound on every channel

Hi.

Lately, I bought Bose S1 PRO PLUS to be able to plug in my microphone (XLR cable) and piano Roland FP10 (only AUX, TRS cable) and play a gig.
I noticed that when the Expanders feature (that acts like a noise gate) is off, every channel gives a hissing sound even when nothing is plugged into the channel. The hiss is stronger when I plug in my piano into the channel.

The higher the channel’s volume is, the stronger the hiss.

I can’t use Expanders and make the channel louder cuz of 2 reasons:

  • they cut off the signal of my piano sometimes
  • there is no his when I’m not playing, just slight distortions but as soon as I hit the key the hiss is big. When I play quietly, his can be louder than my piano when the channel’s volume is from 50%-80%

The channel with the mic has the Expanders turned ON and it works without any problem.

Tried different solutions: making the channel lower, the piano louder and the opposite, changing channels by adding the adapter to the AUX cable, and such. I also tried to take out the battery - no difference.

I now think that it’s the BOSE’s problem but I’m not sure if it’s a bug or a feature.

Does anyone have the same experience, know the workaround, or at least tell me if I need to send it back?

Connected my T8S to my S1 Pro+ (hadn’t used the T8S in a long while).

Get a scratchy hiss on Ch.1 and 2 if I connect a balanced cable to either channel. This did not happen the last time that I used my T8S with the S1 Pro+.

I’ve tried different cables. I’ve tried the XLR main and the TRS main out ports from the T8S to the S1 Pro+. Same result each time.

As soon as I connect a mic or guitar to the T8S and send a signal, the signal light on the T8S comes on with almost a steady green (indicating signal) and I can hear the scratchy hiss.

Using a Behringer mixer to connect (with the same cables) produces no such sound on the S1 Pro+. It only happens with the T8S.

I switched scenes to the Factory Settings scene but it made no difference. Still got the scratchy hiss. Tried turning the Expanders on and off at the S1 Pro+. It made no difference to the offending sound.

I’m now at my wits end - unable to figure out why this sound is coming out of the S1 Pro+.

The only thing I haven’t done is to do a hard ‘reset’ of the T8S to factory settings. The manual doesn’t tell me how to do that … I’m hoping that someone here will let me know.

I did a reset on the S1 Pro+. I even took the battery out for a couple of minutes, hoping that a reset on the S1 Pro+ would somehow fix this problem. I just don’t know how to do a similar reset on the T8S.

Any suggestions or ideas on how to troubleshoot this problem are more than welcome. It’s driving me crazy.

Thanks.