So below is a video of when we try to start the car, we were told we'd need to tow start it after the rebuild so we thought we'd atleast try key start, so after cranking this sound is near immediate and stops onces key is turned off. Happened after a battery relocation to the boot. I ran 35mm cable for positive and negative and it's still reading 12v at the front and in plugs, so am assuming that is done correctly. The sound is coming from under the intake from the sounds, am running apexi power fc ecu and the 'rats nest' was trimmed down so some solenoids were removed that aren't being used, since the car is single turbo now.
Thanks in advance.

https://youtu.be/t0d0V_duvFk

 

Wow, never heard that before. My approach would be to start unplugging things until the sound stopped just to narrow it down to a specific component. What work was done to the actual engine harness? When removing stuff from the rats nest you have to be careful with cutting things out of the harness. Some of that stuff is actually tied into other things and when you remove it, that signal is no longer being....... sent. Or something like that. Anyway, get it to make that sound and start unplugging things until it's isolated. You could probably get better help from there.

 

Not sure, but sound like spark plug wire arching.

 

Unsure what was actually removed as a Auto Electrician done it for me and they had the car running in their shop. I didn't actually do the trimming myself. The sound EVENTUALLY goes away after a minute or two slowly dims in sound till it's gone so maybe air pressure?? There are a couple points that aren't plugged into anything and are still having voltage run through them, but can't find anywhere to plug them. Have been off since I got the car back from Electrician. But yeah, have had one person say it could be fuel pump vibrations but that doesn't make sense when the rubber fuel lines would diminish any vibrations. I will try your method but gonna have to take intake off so might pull plugs and leads check all those again. Hopefully have a specialist here come have a look.

Thank in advance! Will post if have found the culprit.

 

Harness was fully re-loomed all wires were pretty much replaced, and useless solenoids (for twin turbos) were removed by auto electrician. the car actually ran in the shop for them from a tow start, but not long as there was a oil leak in the sump. So once they finished their work I bought the car home fixed oil leak and done battery relocation, tried starting it after that and didn't start and this sound started. But there is a cable with 2 points on it we can't find where they go, one has a fluctuating voltage running through it and other one is dead. looks as though it plugs in somewhere on drivers side (NZ so right side) from length of the cable it is. Will be pulling plugs and leads out on the weekend coming up, make sure they're all fine if it continues then I'll try your method and start removing rats nests solenoids and isolating it. Thanks for the input guys hopefully it's sorted soon.