I spent a lot of time with my grandmother over the years. My parents and I always went "home" as often as we could. Her house used to sit up on a hill all by itself, and from the road it looked a little spooky especially at night. When I was younger I spent my summers with her and I would hear noises in the middle of the night, but I always thought it was my imagination. I heard what sounded like someone walking down the hall several times over the years and whispers as if someone was talking about something I wasn't supposed to hear. I thought it was my grandma and grandpa talking while they were laying in bed and the only reason I could hear was because my room was across the hall from theirs. The thing that freaked me out the most was the night I was laying awake unable to sleep and I heard what sounded like someone moving things around on the kitchen counters. I immediately got up and locked my bedroom door. I never said anything to my grandma because I figured she'd think it was my mind working over time.
On one of our four day weekends my parents and I drove up to grandma's house. I was 16 years old at the time and really wanted to spend the weekend at home and hang out with my boyfriend so when the phone rang later that night I ran to answer it figuring it was him. I picked up the receiver and said hello as I usually would, since I had no way of knowing who it was as my grandma didn't have caller i.d. I didn't get an answer so I said hello again, and this time I got static like when you turn your t.v. To a channel that has no reception. I said hello a couple more times and then hung up. I figured it was just a bad connection and if it was important they would call back.
I decided to go get a shower and hoped he would call me soon. As I was getting dressed the phone rang again so I ran to my room to answer it thinking it was him. I picked it up and said hello, and all I heard was static again but it was louder this time. I listened for a minute or so still thinking it was a bad connection and then it stopped and I heard the tone you get when someone hangs up on you.
I hung the phone up and went out to the living room and told my dad about it thinking someone was prank calling us. There really wasn't a lot we could do anyways since we had no way of knowing who it was but my dad said he'd answer it from then on. Eventually my boyfriend called and I put it in the back of my mind.
We had a good weekend but it passed quick and before I knew it we were getting ready to go back to Florida. I remember I had just gotten dressed and pulled my suitcase into the living room for my dad to pack when we got done with breakfast. We were sitting down eating and waiting for my aunt and cousins to come over before we left so when the doorbell rang that's who we expected to see when my mom opened the door, but no one was there. She said Dee run out to the laundry room and see if they're at that door and when I opened it again, no one was there.
I walked back into the living room alone and my mom looked at me funny and looked at my dad like what is going on? He went out the front to see if anyone was there and he didn't find anyone. I pulled my mom aside and told her about the phone calls a few nights before and now the doorbell ringing when no one was there, it was weird. She was concerned about someone trying to see who was home so they could break in. There had been a few attempts over the years. My grandpa and my dad both checked to see if maybe there was a short in the doorbell and they couldn't find anything wrong. In fact it never shorted out the rest of the time my grandma lived there. If it had just been the phone calls alone I wouldn't really think much of it, but add the doorbell in and it just doesn't make sense.
There were several other things that occurred over the years that I had put in the back of my mind up until I had the visitor in my room and started to become aware of things. I know now that it was happening to me and around me for far longer than I knew.
All this aside your grandmother's house could also be in an area high in limestone, quartz or granite and this along with water that runs above and underground can cause these manifestations more frequently because it's like a big battery effect. Not sure if any of this is the cause of what's happening at that house but it's some of the theories. Doesn't sound like it's anything that is menacing, so I wouldn't worry about it. Go with the flow and don't fear it.