During the winter months I always keep a space heater plugged in and turned to "Low" in my teaching studio. I was happy to learn from Linda, my regular piano technician that my piano held pitch well since it's last tuning. This is likely due to my diligent attention to regulating the temperature in the room the instrument is housed in.
A number of my students have noticed in recent months a sporadic buzzing when playing an "A" in the higher range of my piano. I noticed it, too. This "sonic wart" became a regular menace to my enjoying playing the instrument. I brought this issue to Linda's attention, she worked on it, and the problem sounds fixed for now. I hope the solution sticks.
Here's the regular PSA ("Piano Service Appeal") that I'll always include at the end of my piano tuning blog posts:
If you are an active pianist, student, or teacher it is essential that you tune your piano at least once yearly. This may strike some readers as excessive, but it is not! Regular piano tunings will increase the longevity of your instrument. Also, annual service on your piano will keep maintenance costs lower. The longer a piano waits between tunings, the greater the work required to restore the instrument to its best functioning. More work = more cost. Make the sensible decision.
The piano tuner I call upon here in the CA bay area is Linda Kay. She provides excellent service and reasonable rates. You can click on her name for her contact information.