[BC] Optimod distortion?

[Dennis Cope]

Need help with a little problem.

I process many 45's and LP's to the hard drive.  Some (most) have clicks and
pops.
I use Adobe Audition to record and de-noise.

The result, although not the best but is acceptable.
When put on the air some of the songs sound like they are running down a
water pipe, sounds bad...

In the studio I checked the output of the board,,,  acceptable
Into the Optimod,,, acceptable
Out of the Optimod,,, water pipe
Into the analogue STL,,, water pipe
Out of the STL,,, water pipe
Into the exciter,,, water pipe
My receiver output,,, water pipe

What is the Optimod doing to the audio?

Dennis
WCTG, WESR