Re: Bosch SKT5102GB fault
If it is a high pitched momentary ‘squeal’ then that will likely be the carbon faced water seal on the circulating pump. That does not indicate a problem and is commonplace.
If the sound relates to it filling with water however it could indicate your water pressure is a little too high and closing the stoptap slightly will reduce that noise.
Whatever the problem may be I wouldn’t worry too much about it at this stage. If it works OK – leave well alone is the way forward. 😉