It is normal for your handheld steamer to produce an intermittent noise along with a trickle of steam when the product is put aside or left to cool down, as it has not fully cooled down yet.
The steam engine is still hot with residual water left in the steam path and this causes the noise. Please allow the appliance to fully cool down (~60 minutes) for the noise to stop.
If this does not solve the problem, please contact us.