I am using a Astron SS30 on my PRO. Had noise at first in the 15-21 Mhz range.....called Astron and they told me to make sure the screws holding the circuit board down were tight (mine were very loose), make sure I was using AC power with a ground and to put a .01 cap across the output. Did these things and my noise disappeared. It has been a very good performer since making these changes. 73 Mike K5UX