Grumbling at child

[Kelpie_mum]

I have 5 y old rescue cream kelpie (Dusty). He has recently started to grumble / low growl at my 3y old in the evenings. Usually occurs when we are (trying) to wind down for the day. Dusty growls/barks when my 3y old talks or bounces around. Its often not even close to where Dusty is resting in his bed. I recognise that perhaps Dusty doesn’t like being disturbed but not sure what to do
any ideas?