Try minding your own fucking business OP. It sounds like the neighbor keeps to themselves so the worse you seem to have to deal with maybe the smell of some dog shit from their backyard.

If you suspect its some type of crime house why the fuck would you send your little brother over to investigate for you pussy?? Grow some balls. Pussy snitch bastard.

Meth lab would stink to high heaven at some point. If its a grow house then head over in the middle of the night and listen outside for the sound of a 60Hz hum from the lamps and ballasts. Its common for growers to have thier lights on cycle set for night time since it helps with heat management. CHeck out the electric meter and see if its running super fast. Look for vent ducts...these are usually hidden as dryer vents of a stove pipe for a furnace or waterheater.

Grow houses make decent neighors IMO. They don't have alot of annoying friends hanging out, mind their own business and are probably pretty mellow. As long as they practice safe electrical procedure there is almost no chance of a fire. Adequate electrical service box, GFI outlets and the ever important "Waist rule", all electrical wires, equipment and outlets should be mounted and insulated above waist level.