[ICOM] 756pro II odd behaviour

[wa6fwf]

Hi All,
   my pro II started something odd tonight,  just below 7Mhz
I will get a pop? chirp? (don't know how to describe it better)
  with each  Hz  change, it peaks around 1.9Mhz
with this noise being 10db plus.
  Disconnecting the antenna  it disappears... and the rig tunes fine...
  If I put a strong wideband noise source on the ant in and the rig 
tunes fine with no popping.
Turning on the attenuator cuts the offending pop?chirp?

Maybe I have a really strong signal overloading the front end?
I have tuned around looking and the only huge signals are the local AM
radio stations but nothing new there as far as I can tell.

Anyone care to take a guess at this?  

Thanks
73
Kevin WA6FWF