[Heathkit] Need SB-303/401 Expert Help Needed.

[OTAKEBI at aol.com]

I have been working an SB-303 SB-401 combo.
What I thought was mic hum is not.
I hooked up another receiver to hear my own signal and I can hear what  seems 
to be a tone
that I can only describe as a spotting tone type of noise when I dead  key 
the mic.
The noise is raspy with a tone that changes frequency as I tune  the 
transmitter with the tuning knob.
If I leave the SB-303 on and unlock the transmitter (SB-401) to make it a  
stand alone transmitter the noise is still there when I dead  key.
If I talk the SSB signal is clear with no flat topping on the  scope.
I have tried different mics and I have tried to use no mic but just  shorting 
the relay to ground.
Noise still there.
I have peaked and nulled the carrier on the board as per the manual with an  
RF probe.
I have checked all tubes with known good subs and with a tube tester.
Set is putting out full output and but for the noise it works  great.
How can I track down such a generalized noise in order to fix the  problem?
Could an expert on this weird problem lead me to solving it.
This does not seem to be a bad ground problem.
Any help would be great since I am stuck and need new ideas.
Thanks,
Dan/N4VET