ghost?

ghost?is it really exist?im believe it but alhamdullilah till now i never see the entities yet.i wish that i will never meet them till the end of my life.okey!actually i want to share some story.it happen last thursday night.i stay up late and do all the washing up because there's have inspection tomorrow.After i clean up everything,im getting tired and ready for bed.At 3 o'clock in the morning suddenly my friend calling me.firstly i just ignore her call.but she keep calling me and with rush she down her bed.i ask her why she act so.she said is it i hear what she was hear.im just keep on silence and i hear a 'knock' sound.i ask her to ignore it but the sound is getting louder.i just ignore it and i continue sleeping.i dont know when the 'knock' sound last.but its quit horror night for me.