let them go to bed with an item of your clothing they can smell you ! Also a ticking clock at the bottem of the cot helps it really does.

Tape record the hoover and play that or some gentle music too, but dont pick them up to hold them just to replace the covers and without talking to them.

Try to sit in another room only go check on them every ten mins or so he/she will get used to it but it may take a few days of consistancy.