[Elecraft] K1 sidetone overpowers headphones

[Robert J Greenwalt Jr]

Don't know if this is an unusual situation or not -- My K1 works fine on
speaker but when I plug in a set of Bose noise cancelling phones the
sidetone during keying becomes an overwhelmingly loud crashing tone in the
phones.  Its almost painfully loud.  When I set the K1 output to zero the
keyer sounds fine in the headphones.  When I turn the power back up to
actually transmit, I get the crashing effect.  Reducing the StL level has no
effect.  The Bose phones have an audio amplifier in the line to produce the
noise cancelling effect -- could RF be causing this?  I'm using a long wire
antenna with the built-in ATU.

Bob