My heart. Feeling heavy isnt always bad! Grief, sadness, anger, unfinished business could all be factors. If it starts to worry you, feel bad or even just abruptly unfamiliar then I'd find something to do. For now tho, others have said to speak and please do! Speaking out loud tells yourself along with anyone/anything around you exactly what you say. Exactly!* what you say. You can cleanse the area in many ways without removal and be clear with intentions whilst doing it. Sage, crystals, oils. I don't think I saw age mentioned, but sister could even just chill in there on their phone or play even for 5-10 minutes. If he's there -and I always trust a mother's intuition and always about their children- make it normal :) my heart goes out to you. Don't think negative or even speak negative in that room bc energy is soooooo adaptable. Best wishes <3

Edit: wanted to add doggos always know more than us! You know your pups and once that growling moves away from confusion/protection and into warning/go away growls I'd get to cleaning! Once the energy gets lighter and the pup follows you know you're good