When I was about 12 and started getting left alone at home, something used to shush me. I'd be pouring cereal, singing along to the TV and suddenly, "shhhhhhh!". First time it happened I absolutely crapped myself and didn't say a word until someone came home. I didn't tell anyone because I didn't think anyone would believe me. I'd even start to convince myself it was just my imagination but then it would happen again. I think it happened about 5 or 6 times.

One Saturday morning I was in my top bunk, the beds were super noisy and the slightest of moves would result in them creaking.

"Shhhhhhh!"

I thought it was my younger sister and decided to annoy her further. I started rocking about in my bunk making as much noise as I possibly could and suddenly

"SHHHHHH!!"

I chuckled, still thinking it was my sister, and then she whispered nervously from below "... Was that you? The shushing, was that you?"

I popped my head down and said "no, it was you". She looked terrified, her eyes welled up with tears and she said "no it wasn't". She ran out of the room crying and wouldn't come back in for a long time. I realised it must have been the shushy ghost and was overcome with relief that I wasn't crazy because someone else had actually bloody heard it.

Haven't heard it since. I'm always kind of waiting. – DentalNylon