Current Transformer problems

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

Hi All,
         This question is for anyone with experience in use of current
transformers and O-scopes. 
I made a quick current transformer by winding 20 ft (~150 turns) of #20 magnet
wire around a 1-inch ID ferrite toroid When I hook it to my scope I get a wave
pattern that is very distorted with overtones, 2f, 4f, etc., and pulses of HF
ringing.
This is on the inlet side of the control box without the coil or cap attached.
The entire lab is lined with grounded wire mesh except the front door.  
1. What am I doing wrong?
2. How can I fix it?
Matt D.