Between uses it is always best to empty the diffuser and give it a quick clean because smells and leftover oils can build ruining the next change of aroma or use.
Always ensure the fan intake is clear of obstruction wherever you site the product
If the unit has got noisier try giving it a thorough clean (as above) and restart it.
Never overfill your diffuser, it can seriously affect performance and lifespan of your product.
If your diffuser runs hot it usually means the product has been overfilled and you should allow it to cool before starting again with water below the fill level.
If your diffuser stops and turns off, check the water level to ensure it is not too low or too high.
Always allow the diffuser to cool after any type of malfunction before cleaning and beginning again with the correct water, clear fan intake etc as this will normally solve your issues.