The ECM is solid state, no relays are inside it. I don't know what could be causing the sound.

The ECU can be bypassed by performing the "Nutter Bypass" which eliminates the ECU from the ignition system. You can do just the timing control part of it, or disconnect the stepper motor in the carb for full ECU disablement.

Here's a link to a wiring diagram showing the change:
http://home.sprynet.com/~dale02/ignmods.htm

Here's a link to a different forum with 15 pages of posts and comments:
http://www.jeepforum.com/forum/f8/how-nutter-bypass-522262/

Note: this mod is not "Smog Legal" and is for trail vehicles only!