I totally understand your frustration. I live in an apt and last year the neighbors had BAND PRACTICE (yep, drums, amps, guitars, screeching into microphones, the works) in the room thats right next to my bedroom. And they would do this in the middle of the night!!!! I asked them politely to stop, then started banging on the wall, then finally called the cops on them. Long battle that didn't end until they moved out. Some people are just rude and selfish.
On the other hand, you mentioned they only do it in the middle of the day when the rest of your neighbors are at work. So maybe they don't realize they're bothering anybody. If they are quiet at night, that seems to indicate they have some respect for the neighborhood. So I suggest what others have said- either call or leave a note and explain it exactly how you did to us. I really wouldn't be afraid to talk to them, esp if you bring your boxer
but I'm not that shy. But a note would be fine too.
If after that they still are loud, then they are a$$***** and deserve to have the police called on them. And I say do it. But I know I would want a neighbor to at least ask me anonymously to stop doing something before having the 5 O show up at my door.
Good luck girl keep us posted.