[Elecraft] RTTY Dual Passband Filter and RFI?

[Ron W3ZV]

I am working the CQ WPX contest. K3 & FL-7000 amp at about 300W. When I 
engage the dual passband filter, I hear a rough buzz, which sounds like 
RFI, on my monitored transmit signal. When I disengage the DPF, my 
signal sounds clean in the monitor. I continue to make contacts, but a 
contest is not a great place for critical signal reports. Any clues?

Ron W3ZV