Dear Nanning,
I have observed the same noises with my 7Bs. I agree with PBB that it is probably from capacitors discharging. It is disturbing but not damaging. There are ways to prevent these sounds, but obviously this was not done for our 7Bs. I am happy not to pay for extra circuitry. I left my 7Bs on virtually all the time anyhow.
I have observed the same noises with my 7Bs. I agree with PBB that it is probably from capacitors discharging. It is disturbing but not damaging. There are ways to prevent these sounds, but obviously this was not done for our 7Bs. I am happy not to pay for extra circuitry. I left my 7Bs on virtually all the time anyhow.

