My springer spaniel that is 18 months old and has started acting strange in the evening. He is a very cuddly and passive dog -- however..
If the telephone rings during the day it has no effect on him; however, if it rings after dark he runs downstairs (like the wind) and sits in the dark. Another odd behaviour is that he growls (grumbles) a fair bit -- only in the evening. Not agression at anyone. He will get up to go outside or to another room and he growls on his way there. You can touch him or talk to him -- he does not show his teath or bite at you, just grumbles.

We do have another springer spaniel (7 years old.) They get along great and play a lot... There is no aggression with either dog toward each other at all...just the one grumbler????