There are over twenty models in the Dyson vacuum cleaner range and each has its own operating manual. While the cause of a high pitch squealing noise has a very likely contender, there are other reasons why your Dyson vacuum cleaner might suddenly sound different.
According to the Dyson DCO1 vacuum cleaner operating manual, a change of pitch in the normal sound of the cleaner can mean a blockage. Depending on your Dyson model, this may be in the mini turbine head, the contact head or the hose. Check any accessible places for blockages, which may be in the form of normal accretions of carpet debris, or an accidentally sucked up object that is causing an obstruction.
Filters need washing
The sound may indicate your filters need washing. Advice varies about how often you should do this as part of your normal maintenance regime, according to your specific Dyson vacuum cleaner model. Generally, however, you should do this about every three to six months. Unplug your vacuum cleaner and remove the filters. Rinse them clean under the tap and squeeze water out. Rinse the filter holder too. Let the items air dry for 12 hours before reusing them.
Filters need changing
For at least one of their models, Dyson suggests you change your filters about four times a year. However, elsewhere, the advice given, for the same model of vacuum cleaner, is that you wash your filters about four times a year and only replace them once a year. To access the filters, lift off the cage and the clear bin. Like most manufacturers, Dyson suggests you use only genuine replacement parts.
Shroud needs cleaning
You may need to clean your shroud. The shroud is a part of the cyclone assembly, having a cylindrical shape and holes in its body. The advice given is to wipe the holes free of dust and debris. However, the illustration shows a hand brushing, not wiping them. You should then inspect the air duct which is located to the rear of the bin. Remove any dust and other debris you discover there.
Work logically through the suggested remedies and if these make no difference, you might want to contact Dyson through their helpline on 0800 954 0154.