One i7 core running hotter than other 3, please help

I just finished building new i7 system. I ran some stress test using prime95 and noticed that one of the core temp is always ~3-4 degree higher than other 3 cores. I first ran just 1 instance of prime95 and then 4 instances of prime95. Is this normal?

Below are the temperature readings from Real Temp 3.00

Idle temp:
38 33 35 34

Full load temp:
62 58 58 58

Your responses would be very much appreciated. Many thanks in advance.

My System:
Intel Core i7 920
OCZ Platinum 6 GB
Gigabyte UD4P X58
GTX 275
WD Black 640 GB and 1 TB
Antec 900 II
Corsair 650 W
Xigmatec Dark Knight
Windows 7 RC 64-bit

Thanks Proximon for your reply. Otherwise I was a bit worried that maybe I have to reinstall the CPU Cooler.