A few people have reported that they get a high pitched string of noise pulses when they change tracks on the Pi, Airport Express, and when changing stations on their TV or cable box. This noise is created when the crystal controlled oscillator on the signal input receiver is still locked to the previous signal stream and is trying to find the start bit of the new digital signal. 

I have had a look at this and inserted a software mute routine to suppress the audio signal until the start bit is found and the oscillator is locked to the correct sample rate of the audio signal.
This solution works for me when tested on a streamer that gives me the same problem.

There might be an additional improvement in the high notes to be heard, but this could just be my imagination.

But I still need it confirmed. So am looking for someone who gets this chirping noise as well, and is familiar with the routine of swapping over the firmware. I just need to know who has the time to double check this for me, and is also in the UK. The latter will cut down on delivery time.
If I get more than one offer of help, I shall have to flip a coin.