Why does my system now have shrill top end.

Yes, the humidity shift happens at about 45%.

Above that it is dissipative. static will bleed off.

Below that, it will begin to build. The effect is subtle but persistent, and worsens as the dryer it becomes.

It's not just the carrier as an issue it's the static.

The next possibility is a degrading of electrical connections, with regard to impedance at the interface, due to oxidation, contact quality degradation, etc.

Next, that some critical component or aspect is right on the ragged edge of being overly revealing and overly analytical. As combinations go, that is.

Anything with outboard power supplies and an umbilical connection to said power supply is especially vulnerable to contact degradation in the connecting umbilical. Check those connections. Reinsert, tighten, etc.

Consider putting noise filters on all the new equipment and lines in the new kitchen.

As well, the person who did the electrical system for the kitchen, may have altered your room’s connectivity to get the kitchen on line.

Consult with them.

those are probably the major potential culprits.

I’m guessing one of the new pieces of equipment in the given kitchen has a very dirty ’pulse power supply’ and is injecting noise into the AC which is impacting your sound space, electrically.

This can be quickly tested via shutting down the new kitchen at the AC power panel, then adding kitchen breakers back in, one by one, listening the whole while. If this is the case, the culprit outlet and associated kitchen gear will show itself. Lighting is also on this list. Especially CCFL’s and LED bulbs.

Best cheap tweak ever for audio shows:

BRING INCANDESCENT BULBS to the show and put them in the bulb sockets of the room, and turn them on.

the filaments of incandescent bulbs will knock down (partially absorb) the noise peaks of the dirty ac power on the given lines in the given hotel room.