Telling a happy (?) ghost experience of mine to offset the hella creepy ones on this thread.
My grandfather passed away in 2013, pretty peacefully may I add but considering how close we were, it was a really difficult death for me and my family. I was driving home for his funeral on a cross-state trip, so I had my iPod plugged in which is filled with 5,000+ songs on shuffle. It had been on shuffle for about 3 or 4 songs when a rock song came on my shuffle. I started singing loudly along with it, and towards the end of the song, I said "Hey Grandpa and Ken (Ken was my step-grandfather who had also just recently passed away), I'm sure you guys would love this! So upbeat!" and not 10 seconds later, the song changed to one of the only polka songs on my iPod. It was You Are My Sunshine by Frankie Yankovic (who was my grandpa's friend and favorite musician, huge polka fan) , and it ended up being weirdly loud for how low I had the volume for the rock song. Needless to say, I cried for a while and said hey.
It could of easily been a coincidence, but considering that I'm a practicing Catholic and it felt so spooky, I felt like it was a nice way for him to say hello.