This just happened to me last weekend. I was at my aunt's house watching her two dogs for her while she and her husband went out of town. They have a little short-legged yellowish dog named Hazel, and a fat old spaniel named Henry.
I was sleeping in my aunt's room when around midnight I heard Hazel jump off the bed and start chasing something around the floor. It sounded like she was playing with a plastic bag. This is not normal behavior for her in the middle of the night.
I was curious to see what she was doing, so I turned the light on. She was in the middle of the bedroom looking very excited, but there was nothing at all there for her to play with. The weird thing is, I could still hear the plastic bag being shaken around! Shooka shooka shooka.
The odd rustling sound seemed to leave the room and go into the dark hallway, where it continued. I worried perhaps the other dog Henry had gotten caught in a grocery sack somehow, and needed my help. At his advanced age he certainly wouldn't play with anything. The sound stopped as I turned on the hallway light, but Henry wasn't there. I found him on the living room couch sleeping peacefully like a fat old angel. As paranoid as I felt, there was nothing to do but return to the bedroom and try to go back to sleep.
In the morning I searched all the rooms for anything that could have made that noise, but I found nothing. When my aunt returned from her trip I asked her if she had ever experienced unexplained sounds in her house. She confided that she frequently hallucinates hearing something run through her bedroom squeaking during the night. This is absurd because her family has never seen the first sign of a rodent during all the years they have lived in their home.
Together we came to the conclusion that what I had heard was only her hallucinated rodent getting stuck in my hallucinated shopping bag!