Edit: The laptops in question were sent back, thank you all who tried to help me.
Hi friends, I'm having a RAM related problem that I cannot diagnose by myself.
So I have 2 laptops (A,B) of same model, and 2 sets of RAMs (X,Y) of different model. (Yes 2 sets and 4 sticks total, but to keep the problem not too messy, I always test them within the same set.)
Originally it's A+X and B+Y. Both exhibit random unstable behaviors (A+X more severe), such as crash and lock up, which I later guessed it's RAM related.
I use Memtest86+ to check: A+X errors a lot, B+Y I forgot...
I exchanged them: both A+Y and B+X have no errors.
I exchanged them back: A+X errors less than first time, B+Y no error.
I cleaned both DIMM and socket with ethanol, not fixed.
Since the randomness, I suspect heat related, but then I tested A+Y with vent blocked, so it's hotter than first test, still no error.
One strange thing is, the errors are all across the address range (unlikely to be real bad/weak cells), but stay constant at the same bit within same test, and shift a little across different test/reboot.
Also I don't understand how it can differ with 2 laptops of exact same model and config.
I'm really lost here, can anyone help me?