When deciding to purchase an air cleaner, as well as looking for a unit that is both affordable and effective for your requirements, it is advisable to check the types of air purifier filters used in the unit and also how much those filters are to replace.
hepa filter
HEPA Quiet Air Purifiers
If you have severe allergies and noise is an issue, then your best bet is to use one of the reasonably quiet air purifiers that use a HEPA filter, such as the Blueair air cleaners.