Ours did it at 4 on Sunday morning because he'd eaten a pig's trotter that disagreed with him. If you want to enjoy your breakfast, I'd recommend not ignoring him on the basis that "he'll stop soon."

On a serious note, assuming it's not anything causing immediate discomfort, I'd guess either separation anxiety or just a bit of attention seeking. I can't help on separation anxiety, but we did really well with our dog's attention seeking barking by using 10 second timeouts (would sin binning be more appropriate here?) out of the room, or even in a different room, as soon as he barked in the flat. Sorted it out a treat.

Yes,and I can list them
Black tripe
Cow heel
Pigs feet
Honeycomb
Shall I continue ?

Sadly most tripe is bleached in the UK. It is better not and in recipies that need frying. Now steak and cowheel pie ... the food of gods.

I remember seeing it delivered,in wooden crates from UCP,I think,and the unbleached parts were green,unsurprisingly.
Looked horrific

We are delving into the realms of D
fantasy here , I don't think it will stop Jasper howling.

It would stop me howling: a pint of Drabs and a steak 'n' cow-heel pie.

Felice Anno Nuovo