Variable fan speeds for no apparent reason

A few weeks ago I had to replace my CPU fan as it was starting to rattle really badly and I decided to change it before it failed completely.
Just before it started rattling, I noticed that it was also tending to run at a higher speed a lot more often than it normally did and I put it down to a worn fan and also gave the system a damn good clean out as well as the heat sink which I regularly clean anyway,
After installing the new fan everything was great, It was so quiet I had to check that it was actually working and the apps/odd old game that I play regularly which were the things that made it work hard stopped happening so I was very happy, But after about 2-3 weeks of doing everything I normally do on my pc the new fan started working at a faster speed when using these particular apps/games which didn't seem to make any sense to me.
I have checked the working temp of the CPU and most of the time it runs at it's ideal temp and sometimes slightly lower and it also doesn't seem to run any hotter even when the fan starts working harder.

I have done a lot of different scans and checks to try and find the problem but had no luck so far.

Could it be that the sensor's or fan controller may be malfunctioning ?, And if so, How would I go about fixing this problem ?.

If you can think of any other things that I can check I would be more than grateful for any help that you can give me.

I should also say that some days it does seem to be worse than others, and also the new fan that I am using is not the same as the original although I would say it is definately a better one than the stock OEM one.

I am also wondering whether the new fan could possibly be running in the wrong direrction and I have tried looking all over the net to find which way it should be working (sucking / blowing) on my system which is a HP Pavillion a6455.uk...From what I can tell it is sucking air in towards the heatsink but everything I have read has all told me that different computers use different methods.

Please help as this is driving me nuts.

What is controlling your fan speed? Your mobo? Or software like SpeedFan?

The Mobo

Usually the hooter the CPU gets , the faster the fan will go.

Sorry to ask this seemingly dumb question could one of you guys try to find whether my CPU fan should suck air onto the heatsink or should it be sucking air away from the heatsink,,,I am asking as I have recently replaced the fan and the new fan is the same size but a lot more powerfull and to start with was spinning totally silently even when it did actually throttle/speed up which rarely haooed. Just lately when I play a certain old online game and also the odd app here and there and due to this I have check with process/performance monitor and everything is just running as normal and there doesn't seem to any high CPU usage that would maybe cerate heat and cause the fan to speed up.
The only reason I am not sure which way the air should be going is because it is a totally different fan as in the original one was plastic and cheap and the new one is in a metal casing. Im pretty sure i can't just flip the fan over as the Blade rotor would rub on the heatsing unless i used a few washers and then out it on..I know that I cannot just change the red and black wiring over to change the direction as I have been told that it wouldn't work as all fans are now manufactured so that they will only spin one way which is starting to make me think that I may have to get another fan if it is spinning in the wrong direction and I know they are cheap enough but I really can't afford it at the moment,