Ok so I had a custom box built for my mini with 2 Kicker CVR comps and a clarion amp. I am not very electronically savvy, so I'm going to try to explain this the best way possible.

After the install. I noticed that on several occasions I would hear a extremely loud feedback sound coming from my subs, this was not immediate, but like several minutes later after getting out of my car.

I took it back to the guys that installed it. They messed around with it and rewired something and this time they said there was no high voltage current that they could tap into that turns off! They installed a button that cuts my subs on and off. Cool that works, but if I leave the switch on I get the feedback a couple minutes after and it kills my battery. Please help!!!

 

That's why they make relays. I'd run far and fast from that shop before they burn your car to the ground.

 

As Blackbomber said, Run and Run Fast these guys obviously do not know how to wire a sub amp properly. You need three things for a sub amp power.

1. Always On High Current Power (this is usually the battery connection)
2. Switched Low Current power (there are a lot of these in the car)
3. Ground. (there is an ample number of spots for this)

If these guys cant get this right then I will say it again Run and Run Fast.

My suggestion is to find another shop and have them take a look at it and pay them to do so.