If you are getting a "pulse", it sounds like it's coming from your air source. What are you using?
Based on my previous experience, I would suspect it's a piston type (or reciprocating) compressor, in which a piston moves back and forth, compressing the air. This may explain your pulse paint pattern.
If you are using a compressor, you may want to look at having an air "accumulator", which would give you a constant, steady air source. The compressor would fill an accumulator tank, and you would regulate the air pressure coming off the tank. A steady source of air should not pulse. You can buy a 5-gallon portable tank at Wal-Mart, I believe they are under $30. You'll need a regulator, if you don't have one.
Or, if money is not a big issue, you could buy a compressor set-up that has a built-in tank. Here is one on e-Bay, which is where I bought mine.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=22662&item=4355578576&rd=1&tc=photo
Good luck!