Hello, this is Ava with Think Crucial.
There are a number of reasons why your Dyson is acting that way. First, it can be due to a battery of the cleaner. Make sure that the power cable is properly plug to the power and seated properly from the unit while charging. If you find that the battery isn't charging at all, you may need to replace the battery. Second is to check the MAX button of your cleaner. If the button lights up and flashes when your Dyson keeps on pulsating, press and hold the power button and depress the MAX button to turn off the function. You may need to do it for a few times to get the hang of it. Third is to check for any blockages or clogs in the attachments. Look down through the tube and check to see if there are clogs on the sweeper end or if the roller is tangled up in fibers. Clean the roller brush are if it it's necessary. You may need to empty the dust bin of your unit as debris can build up in hard to reach places. Lastly, cleaning the filters may fix the pulsating of your cleaner. Remove the filter and rinse it with cold water and air dry it for 12 hours. Don't use detergent when washing your filters. If the pulsating doesn't go with the given quick fix, I suggest to contact Dyson for further assistance on this.
You can purchase a wide variety of high quality Dyson replacement parts for your Dyson Vacuum direct from Think Crucial with free shipping and an exclusive 10% coupon for Fixya.com readers, use code: FIXYA10
I hope this was helpful.
Think Crucial Customer Care