If I recall, pulsing is usually sign of a blockage. Either a partial one or where it completely clogged. Our V10 even shows a light indicating just that. 

@DavidTaylor explained in another post, that when you’re using boost it forces more power, equating to a higher air wattage. This I suspect is bypassing whatever the cause is. 

What light is your machine showing? Have you checked their website for help? 

My cordless vacuum cleaner is making a pulsing noise, what does this mean? | Dyson Community

Support | Troubleshooting | Dyson 

I’d also suggest checking if it still pulsing with the stick removed? It is doesn’t your culprit is in the stick or cleaner head.

The fix for this is a $111 main body. It is apparently an electronic failure that happens more than Dyson would like to admit. They charge for the main body when your issue is outside of warranty.  This is probably the best option due to the price for a new vacuum. They do make it easy to order through chat, etc.

I had the same problem. Dyson gave me a new main body for free and it solved the problem. My vac is 7 months out of warranty. On the delivery note was a price of $399!

Hello, @HajiAslan could you please tell us about what happened after? I have the same issue and everywhere says it is either a blockage or a main body problem. If it can be a real blockage I will disassemble all and clean everything but if it is a main body problem I am wondering if it is the motor part or the cyclone part. The reason I am wondering: I can get the cyclone part for a much cheaper price as the warranty has just finished. I have the exact same problem with yours and I think the blockage sound is a little different than this. Also, I can add another detail: it works normally if I block the airway about halfway and that is another reason I start to think it is not about blockage. Thank you so much. BTW I would appreciate any other opinion/idea/help. 

Hi,

to answer your question: After taking everything apart and cleaning all the parts it still did not work. I contacted Dyson about my problem and they sent me a main body replacement. Everything works fine since then. My warranty had just finished but they gave me the part for free.