A howl is a long-distance call, not a protest
Howling is how dogs call across distance, so a dog who howls at an empty house is usually trying to locate his people or answer sounds he hears outside, from other dogs to sirens passing on the road. The timing separates the causes. Howling that starts within minutes of your leaving, especially with pacing, drooling or door scratching, belongs with separation unease. Howling that erupts at the same external trigger each day, in an otherwise settled dog, is a reply, and the empty house simply means nobody is there to tell him the conversation is over. Either way, he never howls to annoy the neighbours, and punishment on your return, hours after the last howl, teaches him nothing except that homecomings are tense.
Get the neighbours' timing before you train
You cannot hear the problem yourself, so borrow ears. Ask the neighbours who mention it, kindly and without defensiveness, when the howling starts, how long a bout lasts and what is happening outside at the time. A simple recording while you are out confirms their report and adds the body language: a dog who howls, then settles to sleep between bouts is in a different place from one who howls continuously while pacing. This timing is the foundation of the plan, because training a dog who panics at the door is different work from reducing the daytime triggers of a dog who answers every siren on the street. It also gives you a baseline to prove progress against later.
Build quiet absences and duller triggers
For the lonely howler, practise departures in the same graded way as any alone-time work: out the door and back before the first howl, growing the gap in uneven steps, with low-key exits and returns so the door itself stops predicting drama. Leave a long-lasting chew or a scattered sniffing game as you go during practice, and keep a radio or television playing at ordinary volume if that is what the house sounds like when you are home. For the reply howler, reduce the trigger instead: close curtains over the window he watches, keep him in the room furthest from the street during the siren-heavy hours and reward the choice to stay quiet through a passing sound with calm praise and a treat, so silence starts to pay.
Protect the peace while the training catches up
Tell close neighbours what you are working on and roughly how long the plan takes; people tolerate a known project far better than a mystery noise, and their updates become your progress reports. For long absences before his tolerance is ready, bridge the gap with a sitter, a walker or a day with a trusted friend rather than leaving him to rehearse hours of howling, because every long, distressed session makes the next one harder. See your vet if the howling is new in an older dog, comes with restlessness at night or appetite changes, since discomfort and confusion can both surface as calling out. Keeping every report and arrangement in one place helps the plan hold together, and KinsLe does that with KinsLe Messenger, the per-pet communications hub where neighbours, sitters and family can update you about your dog in a single thread.