Distinguish harmonic sounds from non-harmonic
A standard difference between harmonic and non-harmonic sounds is that harmonic sounds tend to be periodic (in the time domain) in nature whereas non-harmonic sounds don't show any periodic properties since they're completely random. 

One initial method you could try is simply performing autocorrelation in the time domain to see whether that portion of your signal is periodic. This could help you differentiate between the different sounds. There are definitely more complicated ways to test this. You could go to the extent of training a machine learning model based on certain features in the audio signal. But maybe you could just give the autocorrelation a try and see how well it performs for your application.