I have a American 155 Forced Air Kerorsene heat

Tis atomizing the fuel so it'll burn hotter/better.
up their loud tis normal.

solution link.........................
Heating and Cooling Toronto Services

Here as link to your DESA International, ALL-Pro heater, Model # PK 60. Be sure to checkout the Trouble Shooting Guide.

http://www.desatech.com/manuals/Construction%20Heaters/113282-01.pdf

I'm sure this will help solve your problem. Please let me know.

There is an igniter module and then the igniter electrodes (check the air gap) that produces the spark to start the fuel burning, both could be defective.

this unit operates with a small air compressor at rear of motor. Remove the solid 1/8 inch plastic plug. install a low pressure gage. you should read around 5 psi

clean all of your filters and the spark plug and go back to useing K1 kerosene. Diesel fuel has a higher ignition temp. burns dirty and has a tendency to gel.

Check your fuel and air lines for leaks, typically it's the CAD flame sensor but if you have already replaced it try checking the high heat limit switch. It looks like a thick watch battery just behind the combustion chamber, take it off and hold a lighter under it. If it's working properly you should hear a faint click when it shuts off, no click then it's bad.

It sounds like the motor may be going out. I suggest you contact Master Parts at 800-446-1446 or you can find them online at www.masterparts.net they should be able to help you find the part you need. I hope this helps!