MBP fan ramps up after waking from sleep

Hey folks. So I've noticed a strange occurrence with my MBP (unibody late 2009 model, 3 weeks old). It's happened since purchase and It's intermittent and hard to isolate, but I'd like to hear if anyone has noticed this too or a potential fix. It could totally be normal.

Essentially what is happening is that my MBP's fan will sometimes ramp up to around 2700rpm after waking from sleep (typical unloaded speed is ~1900rpm). It will then slowly speed down to the typical fan speed a couple minutes afterwards. It seems that it occurs only in battery mode and when:
a) It is used on material surface, ie couch or bed OR
b) It is woken quickly after entering sleep

I haven't noticed this happening when plugged into AC, perhaps because it's always on a desk when on AC?

What I've done to try to solve the problem: resetting the PRAM, logic, etc, reinstalled the OS (in case a software issue).

Obviously this is not a huge problem, but it's a bit of a nuisance. Anyone have any ideas?

 

sometimes if it was really hot before it slept, it starts spinning back up, just in case it still is... if its like right away... running on a soft surface that holds heat will make the laptop run much hotter. In fact you shouldn't run it like that at all because it can cause it to overheat and get damaged.

if it takes a few seconds to do it, it could be some program you have running that does something when it wakes back up and hits the CPU to 100% for a minute, so it spins up... like its supposed to...

overall, 2700 rpm isn't much to worry about.. maybe if it was going up to like 5000 or 6000

 

Thanks for the suggestion doh123, and although it could possibly be a cause, in my case the CPU was actually running quite cool, so I'm not sure if it's a contribution factor.

Update: Called up Apple and one of the tech reps found documentation stating that when running of battery, the MBP (or other laptops I imagine) will run with fewer processes and thus will take a bit longer to control the fan speed after waking from sleep, hence why the fan ramps up immediately, then slowly dies down over time.

I'm not quite sure what to think of this, but it seems logical nevertheless.

 

the SMC tries to control it smartly... it doesn't just react to temps all the time, sometimes you'll notice it not changing when you think it should because it often tries to go by what it think will happen... but I don't think their logic in it is that great, and sometimes doesn't react perfectly.