I keep seeing.."him"? What do I do?

Okay, I'm 13 (female) and my dining room and kitchen are fully visible from the living room..Well sometimes I sleep in the living room or come out at like 3 AM for a drink, and everything I do..I hear footsteps..then a..kinda..dunno how to describe it..it's a weird noise..like "gruuuuuuu" in a deep voice..then I faintly hear "alllly......" and there is nobody in my house named Aly, I also see a figure walking around my house at night..The creepiest part? Since there is no Aly in my house, I asked my mom about the house history, so we looked it up, and what was so freaky, The last people who lived here was Derek and Aly Johnson, and Aly left Derek and Derek died IN THE DINING ROOM!!!! (of a heart attack) what do I do!? I only recently started to see and hear him.