MacBook Pro 13 - fan jumps to 6000 rpm when laptop sits flat

[Xploit12]

I've recently repaired a water damaged MacBook Pro 13" that came without a hard drive. I bought a 60GB one just to load OS X and test it following the repair and everything works fine except the fan jumps to 6000+ rpm when the laptop sits on the desk but when I tilt it forward it slows back to 2000+ rpm. No over heating issues as it happens from the moment I switch it on... Any ideas anyone?

 

[NazgulRR]

A misaligned fan? Open it up and check if it's seated correctly and re-tighten its screws.

 

[Xploit12]

I took the back off and had a look, everything seems fine there but I've since found the "kernal_task" ramps up to 98% CPU usage which is why the fan kicks in, but when I turn the laptop upside down then it goes back to normal?! WTF!?