you can take the battery down to super cheap auto and they do a free battery test with a full print out.

I had the same issue in my S15 back in the day. Turns out the battery randomly dropped a cell on the negative terminal side which lead me to think it was an earthing issue.

From memory the ECU doesnt have a "relay" just a fuse, what your hearing might be the starter relay or the tick might be the solanoid on the starter triggering. (possibly the fuel pump relay too however it doesnt sound like a fuel issue here)

easiest thing to do is test the battery as its free and costs nothing then if that checks out go from there.

Gotta love cars

1 problem could be caused by 100 different things Click here to enlarge