MacBook beeping differently with different combinations of RAM.

I recently purchased new RAM Chips from Corsair (2x4GB DDR3 1066MHz). When I replaced the old memory (2GB) with the new memory and turned my computer on, the screen didn’t turn on and the MacBook started beeping once every 5 seconds. I read around here that it means that the RAM isn’t detected.

I tried different combinations with the old RAM and the new RAM and I even tried putting every RAM stick at once in every slot. I found out that each one of the new memory sticks works when it’s installed at the top slot only, with the bottom slot either empty or with the old 2GB RAM sticks.

Another weird thing is when I place the new 4GB stick at the bottom slot and the old 2GB stick at the top slot, my MacBook beeps 3 short beeps, 3 long beeps, 3 short beeps. Also, when I place the new 4GB RAM stick at the bottom slot with the top slot empty, the computer doesn’t recognise the RAM, giving me 1 long beep every 5 seconds. Once it even gave me 3 beeps the same length on repeat.

It’s kind of confusing so I’ll put it this way:

4GB RAM on the top, 4GB RAM on the bottom - 1 long beep every 5 seconds

4GB on the top, 2GB on the bottom - works

4GB on the top, empty on the bottom - works

2GB on the top, 4GB on the bottom - 3 short beeps, 3 long beeps, 3 short beeps.

empty on the top, 4GB on the bottom - 1 long beep every 5 seconds.

Any thoughts on what could it be? I don’t think the new RAM is faulty, because each one of them works in the top slot. It seems like the bottom slot cannot handle 4GB of RAM.